From 75c953a1d50cd707e2afe4dd46888056a71eb501 Mon Sep 17 00:00:00 2001
From: Abigail <abigail@abigail.be>
Date: Mon, 19 Apr 2021 13:49:21 +0200
Subject: README.md for week 109

---
 challenge-109/abigail/README.md | 105 +++++++++++++++++++---------------------
 1 file changed, 51 insertions(+), 54 deletions(-)

diff --git a/challenge-109/abigail/README.md b/challenge-109/abigail/README.md
index 32dc7d1d9d..860949d790 100644
--- a/challenge-109/abigail/README.md
+++ b/challenge-109/abigail/README.md
@@ -1,70 +1,67 @@
 # Solutions by Asbigail
-## [Locate Memory](https://perlweeklychallenge.org/blog/perl-weekly-challenge-108/#TASK1)
+## [Chowla Numbers](https://perlweeklychallenge.org/blog/perl-weekly-challenge-109/#TASK1)
 
-Write a script to declare a variable or constant and print it's
-location in the memory.
+Write a script to generate first 20 Chowla Numbers, named after,
+Sarvadaman D. S. Chowla, a London born Indian American mathematician.
+It is defined as:
+
+    C(n) = (sum of divisors of n) - 1 - n
+
+### Output
+
+    0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21
 
 ### Solutions
-* [C](c/ch-1.c)
-* [Fortran](fortran/ch-1.f90)
-* [Go](go/ch-1.go)
-* [Pascal](pascal/ch-1.p)
-* [Perl](perl/ch-1.pl)
-* [Python](python/ch-1.py)
-* [R](r/ch-1.r)
-* [Ruby](ruby/ch-1.rb)
 
 ### Blog
-[Locate Memory](https://abigail.github.io/HTML/Perl-Weekly-Challenge/week-108-1.html)
 
 
-## [Bell Numbers](https://perlweeklychallenge.org/blog/perl-weekly-challenge-108/#TASK2)
+## [Four Squares Puzzle](https://perlweeklychallenge.org/blog/perl-weekly-challenge-109/#TASK2)
+
+You are given four squares as below with numbers named `a`, `b`,
+`c`, `d`, `e`, `f`, `g`.
+
+              (1)                    (3)
+        ╔══════════════╗      ╔══════════════╗
+        ║              ║      ║              ║
+        ║      a       ║      ║      e       ║
+        ║              ║ (2)  ║              ║  (4)
+        ║          ┌───╫──────╫───┐      ┌───╫─────────┐
+        ║          │   ║      ║   │      │   ║         │
+        ║          │ b ║      ║ d │      │ f ║         │
+        ║          │   ║      ║   │      │   ║         │
+        ║          │   ║      ║   │      │   ║         │
+        ╚══════════╪═══╝      ╚═══╪══════╪═══╝         │
+                   │       c      │      │      g      │
+                   │              │      │             │
+                   │              │      │             │
+                   └──────────────┘      └─────────────┘
 
-Write a script to display top 10 Bell Numbers. Please refer to
-[wikipedia page](https://en.wikipedia.org/wiki/Bell_number) for
-more informations.
+Write a script to place the given unique numbers in the square box
+so that sum of numbers in each box is the same.
 
 ### Example
-* `B_0 = 1`, as you can only have one partition of zero element set
-* `B_1 = 1`, as you can only have one partition of one element set {a}.
-* `B_2 = 2`, `{a}{b}`, `{a,b}`.
-* `B_3 = 5`, `{a}{b}{c}`, `{a,b}{c}`, `{a}{b,c}`, `{a,c}{b}`, `{a,b,c}`.
-* `B_4 = 15`, `{a}{b}{c}{d}`, `{a,b,c,d}`, `{a,b}{c,d}`, `{a,c}{b,d}`,
-              `{a,d}{b,c}`, `{a,b}{c}{d}`, `{a,c}{b}{d}`, `{a,d}{b}{c}`,
-              `{b,c}{a}{d}`, `{b,d}{a}{c}`, `{c,d}{a}{b}`, `{a}{b,c,d}`,
-              `{b}{a,c,d}`, `{c}{a,b,d}`, `{d}{a,b,c}`
+
+~~~~
+Input: 1,2,3,4,5,6,7
+
+Output:
+
+    a = 6
+    b = 4
+    c = 1
+    d = 5
+    e = 2
+    f = 3
+    g = 7
+
+    Box 1: a + b = 6 + 4 = 10
+    Box 2: b + c + d = 4 + 1 + 5 = 10
+    Box 3: d + e + f = 5 + 2 + 3 = 10
+    Box 4: f + g = 3 + 7 = 10
+~~~~
 
 ### Solutions
-* [AWK](awk/ch-2.awk)
-* [Bash](bash/ch-2.sh)
-* [BASIC](basic/ch-2.bas)
-* [bc](bc/ch-2.bc)
-* [Befunge-93][befunge-93/ch-2.bf93]
-* [C](c/ch-2.c)
-* [Cobol](cobol/ch-2.cb)
-* [Csh](csh/ch-2.csh)
-* [Erlang](erlang/ch-2.erl)
-* [Forth](forth/ch-2.fs)
-* [Fortran](fortran/ch-2.f90)
-* [Go](go/ch-2.go)
-* [Java](java/ch-2.java)
-* [Lua](lua/ch-2.lua)
-* [m4](m4/ch-2.m4)
-* [Node.js](node/ch-2.js)
-* [Ocaml](ocaml/ch-2.ml)
-* [Pascal](pascal/ch-2.p)
-* [Perl](perl/ch-2.pl)
-* [PHP](php/ch-2.php)
-* [PostScript](postscript/ch-2.ps)
-* [Python](python/ch-2.py)
-* [R](r/ch-2.r)
-* [Rexx](rexx/ch-2.rexx)
-* [Ruby](ruby/ch-2.rb)
-* [Scheme](scheme/ch-2.scm)
-* [sed](sed/ch-2.sed)
-* [SQL](sql/ch-2.sql)
-* [Tcl](tcl/ch-2.tcl)
 
 ### Blog
-[Bell Numbers](https://abigail.github.io/HTML/Perl-Weekly-Challenge/week-108-2.html)
 
-- 
cgit 


From 610ff9605ec7b308051a8f04f9b21d6f4060a8cd Mon Sep 17 00:00:00 2001
From: Abigail <abigail@abigail.be>
Date: Mon, 19 Apr 2021 20:16:47 +0200
Subject: Solutions in 29 languages for week 109, part 1.

---
 challenge-109/abigail/README.md            | 29 ++++++++++++++++
 challenge-109/abigail/awk/ch-1.awk         | 37 +++++++++++++++++++++
 challenge-109/abigail/bash/ch-1.sh         | 35 ++++++++++++++++++++
 challenge-109/abigail/basic/ch-1.bas       |  9 +++++
 challenge-109/abigail/bc/ch-1.bc           | 10 ++++++
 challenge-109/abigail/befunge-93/ch-1.bf93 |  2 ++
 challenge-109/abigail/c/ch-1.c             | 53 ++++++++++++++++++++++++++++++
 challenge-109/abigail/cobol/ch-1.cb        | 14 ++++++++
 challenge-109/abigail/csh/ch-1.csh         | 11 +++++++
 challenge-109/abigail/erlang/ch-1.erl      | 15 +++++++++
 challenge-109/abigail/forth/ch-1.fs        |  5 +++
 challenge-109/abigail/fortran/ch-1.f90     | 12 +++++++
 challenge-109/abigail/go/ch-1.go           | 15 +++++++++
 challenge-109/abigail/java/ch-1.java       | 13 ++++++++
 challenge-109/abigail/lua/ch-1.lua         | 43 ++++++++++++++++++++++++
 challenge-109/abigail/m4/ch-1.m4           |  1 +
 challenge-109/abigail/node/ch-1.js         | 45 +++++++++++++++++++++++++
 challenge-109/abigail/ocaml/ch-1.ml        |  9 +++++
 challenge-109/abigail/pascal/ch-1.p        | 13 ++++++++
 challenge-109/abigail/perl/ch-1.pl         | 51 ++++++++++++++++++++++++++++
 challenge-109/abigail/php/ch-1.php         | 11 +++++++
 challenge-109/abigail/postscript/ch-1.ps   | 10 ++++++
 challenge-109/abigail/python/ch-1.py       | 39 ++++++++++++++++++++++
 challenge-109/abigail/r/ch-1.r             |  9 +++++
 challenge-109/abigail/rexx/ch-1.rexx       |  9 +++++
 challenge-109/abigail/ruby/ch-1.rb         | 44 +++++++++++++++++++++++++
 challenge-109/abigail/scheme/ch-1.scm      |  9 +++++
 challenge-109/abigail/sed/ch-1.sed         | 12 +++++++
 challenge-109/abigail/sql/ch-1.sql         |  9 +++++
 challenge-109/abigail/t/ctest.ini          | 35 ++++++++++++++++++++
 challenge-109/abigail/t/input-1-1          |  1 +
 challenge-109/abigail/t/input-1-2          |  0
 challenge-109/abigail/t/input-1-3          |  0
 challenge-109/abigail/t/input-1-4          |  0
 challenge-109/abigail/t/output-1-1.exp     |  1 +
 challenge-109/abigail/t/output-1-2.exp     |  1 +
 challenge-109/abigail/t/output-1-3.exp     |  1 +
 challenge-109/abigail/t/output-1-4.exp     |  1 +
 challenge-109/abigail/tcl/ch-1.tcl         |  9 +++++
 39 files changed, 623 insertions(+)
 create mode 100644 challenge-109/abigail/awk/ch-1.awk
 create mode 100644 challenge-109/abigail/bash/ch-1.sh
 create mode 100644 challenge-109/abigail/basic/ch-1.bas
 create mode 100644 challenge-109/abigail/bc/ch-1.bc
 create mode 100644 challenge-109/abigail/befunge-93/ch-1.bf93
 create mode 100644 challenge-109/abigail/c/ch-1.c
 create mode 100644 challenge-109/abigail/cobol/ch-1.cb
 create mode 100644 challenge-109/abigail/csh/ch-1.csh
 create mode 100644 challenge-109/abigail/erlang/ch-1.erl
 create mode 100644 challenge-109/abigail/forth/ch-1.fs
 create mode 100644 challenge-109/abigail/fortran/ch-1.f90
 create mode 100644 challenge-109/abigail/go/ch-1.go
 create mode 100644 challenge-109/abigail/java/ch-1.java
 create mode 100644 challenge-109/abigail/lua/ch-1.lua
 create mode 100644 challenge-109/abigail/m4/ch-1.m4
 create mode 100644 challenge-109/abigail/node/ch-1.js
 create mode 100644 challenge-109/abigail/ocaml/ch-1.ml
 create mode 100644 challenge-109/abigail/pascal/ch-1.p
 create mode 100644 challenge-109/abigail/perl/ch-1.pl
 create mode 100644 challenge-109/abigail/php/ch-1.php
 create mode 100644 challenge-109/abigail/postscript/ch-1.ps
 create mode 100644 challenge-109/abigail/python/ch-1.py
 create mode 100644 challenge-109/abigail/r/ch-1.r
 create mode 100644 challenge-109/abigail/rexx/ch-1.rexx
 create mode 100644 challenge-109/abigail/ruby/ch-1.rb
 create mode 100644 challenge-109/abigail/scheme/ch-1.scm
 create mode 100644 challenge-109/abigail/sed/ch-1.sed
 create mode 100644 challenge-109/abigail/sql/ch-1.sql
 create mode 100644 challenge-109/abigail/t/ctest.ini
 create mode 100644 challenge-109/abigail/t/input-1-1
 create mode 100644 challenge-109/abigail/t/input-1-2
 create mode 100644 challenge-109/abigail/t/input-1-3
 create mode 100644 challenge-109/abigail/t/input-1-4
 create mode 100644 challenge-109/abigail/t/output-1-1.exp
 create mode 100644 challenge-109/abigail/t/output-1-2.exp
 create mode 100644 challenge-109/abigail/t/output-1-3.exp
 create mode 100644 challenge-109/abigail/t/output-1-4.exp
 create mode 100644 challenge-109/abigail/tcl/ch-1.tcl

diff --git a/challenge-109/abigail/README.md b/challenge-109/abigail/README.md
index 860949d790..57a25f7869 100644
--- a/challenge-109/abigail/README.md
+++ b/challenge-109/abigail/README.md
@@ -12,6 +12,35 @@ It is defined as:
     0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21
 
 ### Solutions
+* [AWK](awk/ch-1.awk)
+* [Bash](bash/ch-1.sh)
+* [BASIC](basic/ch-1.bas)
+* [bc](bc/ch-1.bc)
+* [Befunge-93][befunge-93/ch-1.bf93]
+* [C](c/ch-1.c)
+* [Cobol](cobol/ch-1.cb)
+* [Csh](csh/ch-1.csh)
+* [Erlang](erlang/ch-1.erl)
+* [Forth](forth/ch-1.fs)
+* [Fortran](fortran/ch-1.f90)
+* [Go](go/ch-1.go)
+* [Java](java/ch-1.java)
+* [Lua](lua/ch-1.lua)
+* [m4](m4/ch-1.m4)
+* [Node.js](node/ch-1.js)
+* [Ocaml](ocaml/ch-1.ml)
+* [Pascal](pascal/ch-1.p)
+* [Perl](perl/ch-1.pl)
+* [PHP](php/ch-1.php)
+* [PostScript](postscript/ch-1.ps)
+* [Python](python/ch-1.py)
+* [R](r/ch-1.r)
+* [Rexx](rexx/ch-1.rexx)
+* [Ruby](ruby/ch-1.rb)
+* [Scheme](scheme/ch-1.scm)
+* [sed](sed/ch-1.sed)
+* [SQL](sql/ch-1.sql)
+* [Tcl](tcl/ch-1.tcl)
 
 ### Blog
 
diff --git a/challenge-109/abigail/awk/ch-1.awk b/challenge-109/abigail/awk/ch-1.awk
new file mode 100644
index 0000000000..6b889ae3a0
--- /dev/null
+++ b/challenge-109/abigail/awk/ch-1.awk
@@ -0,0 +1,37 @@
+#!/usr/bin/awk
+
+#
+# See ../README.md
+#
+
+#
+# Run as: awk -f ch-1.awk [plain | compute]
+#
+
+function divisor_sum (n, i) {
+    sum = 0
+    for (i = 2; i < n; i ++) {
+        if (n % i == 0) {
+            sum += i
+        }
+    }
+    return (sum)
+}
+
+BEGIN {
+    COUNT = 20
+    if (!ARGV [1] || ARGV [1] != "compute") {
+        print "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21"
+    }
+    else {
+        for (i = 1; i <= COUNT; i ++) {
+            if (i > 1) {
+                printf ", ";
+            }
+            printf "%d", divisor_sum(i)
+        }
+        printf "\n";
+    }
+    delete ARGV
+}
+
diff --git a/challenge-109/abigail/bash/ch-1.sh b/challenge-109/abigail/bash/ch-1.sh
new file mode 100644
index 0000000000..d4eec1f2d9
--- /dev/null
+++ b/challenge-109/abigail/bash/ch-1.sh
@@ -0,0 +1,35 @@
+#!/bin/sh
+
+#
+# See ../README.md
+#
+
+#
+# Run as: bash ch-1.sh [plain | compute]
+#
+
+set -f
+
+COUNT=20
+
+function divisor_sum () {
+    sum=0
+    local i
+    for ((i = 2; i < n; i ++))
+    do  if   ((n % i == 0))
+        then ((sum += i))
+        fi
+    done
+}
+
+if   [ "X$1" != "Xcompute" ]
+then echo "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21"
+else for ((n = 1; n <= COUNT; n ++))
+     do  if   ((n > 1))
+         then printf ", "
+         fi
+         divisor_sum $n
+         printf $sum
+     done
+     echo ""
+fi
diff --git a/challenge-109/abigail/basic/ch-1.bas b/challenge-109/abigail/basic/ch-1.bas
new file mode 100644
index 0000000000..2af64900eb
--- /dev/null
+++ b/challenge-109/abigail/basic/ch-1.bas
@@ -0,0 +1,9 @@
+010 REM 
+020 REM See ../README.md
+030 REM 
+
+040 REM 
+050 REM Run as: basic ch-1.bas
+060 REM 
+
+100 PRINT "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21"
diff --git a/challenge-109/abigail/bc/ch-1.bc b/challenge-109/abigail/bc/ch-1.bc
new file mode 100644
index 0000000000..4c739fdd23
--- /dev/null
+++ b/challenge-109/abigail/bc/ch-1.bc
@@ -0,0 +1,10 @@
+#
+# See ../README.md
+#
+
+#
+# Run as: bc ch-1.bc
+#
+"0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21
+"
+quit
diff --git a/challenge-109/abigail/befunge-93/ch-1.bf93 b/challenge-109/abigail/befunge-93/ch-1.bf93
new file mode 100644
index 0000000000..e5f947956f
--- /dev/null
+++ b/challenge-109/abigail/befunge-93/ch-1.bf93
@@ -0,0 +1,2 @@
+< v,_@#:<   "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21" +55
+  >     ^
diff --git a/challenge-109/abigail/c/ch-1.c b/challenge-109/abigail/c/ch-1.c
new file mode 100644
index 0000000000..e6716c148a
--- /dev/null
+++ b/challenge-109/abigail/c/ch-1.c
@@ -0,0 +1,53 @@
+# include <stdlib.h>
+# include <stdio.h>
+# include <string.h>
+
+/*
+ * See ../README.md
+ */
+
+/*
+ * Run as: cc -o ch-1.o ch-1.c; ./ch-1.o [plain | compute]
+ */
+
+# define PLAIN    0
+# define COMPUTE  1
+
+# define COUNT   20
+
+typedef int number;  /* Change if we want large numbers */
+# define fmt "%d"
+
+number divisor_sum (number n) {
+    number sum = 0;
+    for (number i = 2; i < n; i ++) {
+        if (!(n % i)) {
+            sum += i;
+        }
+    }
+    return (sum);
+}
+
+int main (int argc, char * argv []) {
+    int type = PLAIN;
+    if (argc > 1) {
+        if (strncmp (argv [1], "compute", 8) == 0) {
+            type = COMPUTE;
+        }
+    }
+
+    if (type == PLAIN) {
+        printf ("0, 0, 0, 2, 0, 5, 0, 6, 3, 7, ");
+        printf ("0, 15, 0, 9, 8, 14, 0, 20, 0, 21\n");
+    }
+    if (type == COMPUTE) {
+        for (number i = 1; i <= COUNT; i ++) {
+            if (i != 1) {
+                printf (", ");
+            }
+            printf (fmt, divisor_sum (i));
+        }
+        printf ("\n");
+    }
+    exit (0);
+}
diff --git a/challenge-109/abigail/cobol/ch-1.cb b/challenge-109/abigail/cobol/ch-1.cb
new file mode 100644
index 0000000000..06a7dcece4
--- /dev/null
+++ b/challenge-109/abigail/cobol/ch-1.cb
@@ -0,0 +1,14 @@
+IDENTIFICATION DIVISION.
+PROGRAM-ID. XXX.
+
+*>
+*> See ../README.md
+*>
+
+*>
+*> Run as: cobc -xF -o ch-1.o ch-1.cb; ./ch-1.o
+*>
+
+PROCEDURE DIVISION.
+    DISPLAY "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21".
+    STOP RUN.
diff --git a/challenge-109/abigail/csh/ch-1.csh b/challenge-109/abigail/csh/ch-1.csh
new file mode 100644
index 0000000000..9a612ffab8
--- /dev/null
+++ b/challenge-109/abigail/csh/ch-1.csh
@@ -0,0 +1,11 @@
+#!/bin/csh
+
+#
+# See ../README.md
+#
+
+#
+# Run as: csh ch-1.csh
+#
+
+echo "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21"
diff --git a/challenge-109/abigail/erlang/ch-1.erl b/challenge-109/abigail/erlang/ch-1.erl
new file mode 100644
index 0000000000..c0b458def9
--- /dev/null
+++ b/challenge-109/abigail/erlang/ch-1.erl
@@ -0,0 +1,15 @@
+%
+% See ../README.md
+%
+
+%
+% Run as: ln ch-1.erl ch1.erl
+%         erl -compile ch1
+%         erl -noshell -s ch1 main -s init stop
+%
+
+-module (ch1).
+-export ([main/0]).
+
+main () ->
+    io:fwrite ("0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21\n").
diff --git a/challenge-109/abigail/forth/ch-1.fs b/challenge-109/abigail/forth/ch-1.fs
new file mode 100644
index 0000000000..8a88bf0b28
--- /dev/null
+++ b/challenge-109/abigail/forth/ch-1.fs
@@ -0,0 +1,5 @@
+\
+\ See ../README.md
+\
+
+.( 0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21)
diff --git a/challenge-109/abigail/fortran/ch-1.f90 b/challenge-109/abigail/fortran/ch-1.f90
new file mode 100644
index 0000000000..be6055f839
--- /dev/null
+++ b/challenge-109/abigail/fortran/ch-1.f90
@@ -0,0 +1,12 @@
+!
+! See ../README.md
+!
+
+!
+! Run as: gfortran -o ch-1.o ch-1.f90; ./ch-1.o
+!
+
+program ch1
+    implicit none
+    write (*, *) "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21"
+end
diff --git a/challenge-109/abigail/go/ch-1.go b/challenge-109/abigail/go/ch-1.go
new file mode 100644
index 0000000000..78d9ca1148
--- /dev/null
+++ b/challenge-109/abigail/go/ch-1.go
@@ -0,0 +1,15 @@
+package main
+
+//
+// See ../README.md
+//
+
+//
+// Run as: go run ch-1.go
+//
+
+import "fmt"
+
+func main () {
+    fmt . Print ("0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21\n")
+}
diff --git a/challenge-109/abigail/java/ch-1.java b/challenge-109/abigail/java/ch-1.java
new file mode 100644
index 0000000000..b50b73f0d2
--- /dev/null
+++ b/challenge-109/abigail/java/ch-1.java
@@ -0,0 +1,13 @@
+//
+// See ../README.md
+//
+
+//
+// Run as: ln ch-1.java ch1.java; javac ch1; java ch1
+//
+
+public class ch1 {
+    public static void main (String [] args) {
+        System . out . print ("0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21\n");
+    }
+}
diff --git a/challenge-109/abigail/lua/ch-1.lua b/challenge-109/abigail/lua/ch-1.lua
new file mode 100644
index 0000000000..5eb2d477f9
--- /dev/null
+++ b/challenge-109/abigail/lua/ch-1.lua
@@ -0,0 +1,43 @@
+#!/opt/local/bin/lua
+
+--
+-- See ../README.md
+--
+
+--
+-- Run as: lua ch-1.lua [plain | compute]
+--
+
+local PLAIN   =  0
+local COMPUTE =  1
+
+local COUNT   = 20
+
+function divisor_sum (n)
+    local sum = 0
+    for i = 2, n - 2 do
+        if   n % i == 0 
+        then sum = sum + i
+        end
+    end
+    return (sum)
+end
+
+local type = PLAIN
+if   #arg >= 1 and arg [1] == "compute"
+then type = COMPUTE
+end
+
+if   type == PLAIN
+then print ("0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21")
+end
+
+if   type == COMPUTE
+then for n = 1, COUNT do
+         if n > 1 
+         then io . write (", ")
+         end
+         io . write (divisor_sum (n))
+     end
+     io . write ("\n")
+end
diff --git a/challenge-109/abigail/m4/ch-1.m4 b/challenge-109/abigail/m4/ch-1.m4
new file mode 100644
index 0000000000..9299e87f97
--- /dev/null
+++ b/challenge-109/abigail/m4/ch-1.m4
@@ -0,0 +1 @@
+0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21
diff --git a/challenge-109/abigail/node/ch-1.js b/challenge-109/abigail/node/ch-1.js
new file mode 100644
index 0000000000..d7cff7b0f5
--- /dev/null
+++ b/challenge-109/abigail/node/ch-1.js
@@ -0,0 +1,45 @@
+#!/usr/local/bin/node
+
+//
+// See ../README.md
+//
+
+//
+// Run as: node ch-1.js [plain | compute]
+//
+
+let PLAIN   =  0
+let COMPUTE =  1
+
+let COUNT   = 20
+
+function divisor_sum (n) {
+    let sum = 0
+    for (let i = 2; i < n; i ++) {
+        if (n % i == 0) {
+            sum += i
+        }
+    }
+    return (sum)
+}
+
+let type = PLAIN
+if (process . argv . length > 2 &&
+    process . argv [2] == "compute") {
+    type = COMPUTE
+}
+
+if (type == PLAIN) {
+    console . log ("0, 0, 0, 2, 0, 5, 0, 6, 3, 7, " +
+                   "0, 15, 0, 9, 8, 14, 0, 20, 0, 21")
+}
+
+if (type == COMPUTE) {
+    for (let i = 1; i <= COUNT; i ++) {
+        if (i > 1) {
+            process . stdout . write (", ")
+        }
+        process . stdout . write (divisor_sum (i) . toString ())
+    }
+    process . stdout . write ("\n")
+}
diff --git a/challenge-109/abigail/ocaml/ch-1.ml b/challenge-109/abigail/ocaml/ch-1.ml
new file mode 100644
index 0000000000..3311ee44fa
--- /dev/null
+++ b/challenge-109/abigail/ocaml/ch-1.ml
@@ -0,0 +1,9 @@
+(*                  *)
+(* See ../README.md *)
+(*                  *)
+
+(*                       *)
+(* Run as: ocaml ch-1.ml *)
+(*                       *)
+
+print_endline "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21";
diff --git a/challenge-109/abigail/pascal/ch-1.p b/challenge-109/abigail/pascal/ch-1.p
new file mode 100644
index 0000000000..c5d97f86bb
--- /dev/null
+++ b/challenge-109/abigail/pascal/ch-1.p
@@ -0,0 +1,13 @@
+Program XXX;
+
+(*                  *)
+(* See ../README.md *)
+(*                  *)
+
+(*                                           *)
+(* Run as: fpc -och-1.out ch-1.p; ./ch-1.out *)
+(*                                           *)
+
+begin
+    writeln ('0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21')
+end.
diff --git a/challenge-109/abigail/perl/ch-1.pl b/challenge-109/abigail/perl/ch-1.pl
new file mode 100644
index 0000000000..64f21d5d24
--- /dev/null
+++ b/challenge-109/abigail/perl/ch-1.pl
@@ -0,0 +1,51 @@
+#!/opt/perl/bin/perl
+
+use 5.032;
+
+use strict;
+use warnings;
+no  warnings 'syntax';
+
+use experimental 'signatures';
+use experimental 'lexical_subs';
+
+#
+# See ../README.md
+#
+
+#
+# Run as: perl ch-1.pl [plain|fetch|compute]
+#
+
+my $COUNT = 20;
+
+my $TYPE_PLAIN   =  0;
+my $TYPE_FETCH   =  1;
+my $TYPE_COMPUTE =  2;
+
+my $type = $TYPE_PLAIN;   # Default
+   $type = $TYPE_FETCH   if @ARGV && $ARGV [0] eq "fetch";
+   $type = $TYPE_COMPUTE if @ARGV && $ARGV [0] eq "compute";
+
+
+
+if ($type == $TYPE_PLAIN) {
+    say "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21";
+}
+elsif ($type == $TYPE_FETCH) {
+    use OEIS;
+    $, = ", ";
+    say oeis (48050 => $COUNT);  # We want the first numbers from
+                                 # sequence A048050.
+}
+elsif ($type == $TYPE_COMPUTE) {
+    use List::Util qw [sum0];
+    $, = ", ";
+    #
+    # Sum the divisors; a divisor has mod 0. This is very inefficient
+    # even for smallish integers, but since we're asked to only 
+    # calculate the first 20 numbers, we don't have to care about
+    # efficiency.
+    #
+    say map {my $n = $_; sum0 grep {!($n % $_)} 2 .. $_ - 1} 1 .. $COUNT;
+}
diff --git a/challenge-109/abigail/php/ch-1.php b/challenge-109/abigail/php/ch-1.php
new file mode 100644
index 0000000000..0516741cc7
--- /dev/null
+++ b/challenge-109/abigail/php/ch-1.php
@@ -0,0 +1,11 @@
+<?php
+    //
+    // See ../README.md
+    //
+
+    //
+    // Run as: php ch-1.php
+    //
+
+    echo "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21\n"
+?>
diff --git a/challenge-109/abigail/postscript/ch-1.ps b/challenge-109/abigail/postscript/ch-1.ps
new file mode 100644
index 0000000000..2ea67f6701
--- /dev/null
+++ b/challenge-109/abigail/postscript/ch-1.ps
@@ -0,0 +1,10 @@
+%!PS
+%
+% See ../README.md
+%
+
+%
+% Run as: ps2ascii ch-1.ps
+%
+
+(0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21) =
diff --git a/challenge-109/abigail/python/ch-1.py b/challenge-109/abigail/python/ch-1.py
new file mode 100644
index 0000000000..6600bda6d5
--- /dev/null
+++ b/challenge-109/abigail/python/ch-1.py
@@ -0,0 +1,39 @@
+#!/opt/local/bin/python
+
+#
+# See ../README.md
+#
+
+#
+# Run as: python ch-1.py [plain | compute]
+#
+
+import sys
+
+COUNT   = 20
+PLAIN   =  0
+COMPUTE =  1
+
+def divisor_sum (n):
+    sum = 0
+    for i in range (2, n):
+        if n % i == 0:
+            sum = sum + i
+    return (sum)
+
+type = PLAIN
+
+if len (sys . argv) > 1 and sys . argv [1] == "compute":
+    type = COMPUTE
+
+
+if type == PLAIN:
+    print ("0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21")
+
+
+if type == COMPUTE:
+    for n in range (1, COUNT + 1):
+        if n > 1:
+            print (", ", end = '')
+        print (divisor_sum (n), end = '')
+    print ("")
diff --git a/challenge-109/abigail/r/ch-1.r b/challenge-109/abigail/r/ch-1.r
new file mode 100644
index 0000000000..1c6165807d
--- /dev/null
+++ b/challenge-109/abigail/r/ch-1.r
@@ -0,0 +1,9 @@
+#
+# See ../README.md
+#
+
+#
+# Run as: Rscript ch-1.r
+#
+
+cat ("0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21\n")
diff --git a/challenge-109/abigail/rexx/ch-1.rexx b/challenge-109/abigail/rexx/ch-1.rexx
new file mode 100644
index 0000000000..3085ab0224
--- /dev/null
+++ b/challenge-109/abigail/rexx/ch-1.rexx
@@ -0,0 +1,9 @@
+/*
+ * See ../README.md
+ */
+
+/*
+ * Run as: rexx ch-1.rexx
+ */
+
+say "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21"
diff --git a/challenge-109/abigail/ruby/ch-1.rb b/challenge-109/abigail/ruby/ch-1.rb
new file mode 100644
index 0000000000..95a38a69cb
--- /dev/null
+++ b/challenge-109/abigail/ruby/ch-1.rb
@@ -0,0 +1,44 @@
+#!/usr/bin/ruby
+
+#
+# See ../README.md
+#
+ 
+#
+# Run as: ruby ch-1.rb [plain | compute]
+#
+
+PLAIN   =  0
+COMPUTE =  1
+
+COUNT   = 20
+
+def divisor_sum (n)
+    sum = 0
+    for i in 2 .. n - 1
+        if   n % i == 0
+        then sum += i
+        end
+    end
+    return sum
+end
+
+type = PLAIN
+
+if   ARGV . length > 0 && ARGV[0] == "compute"
+then type = COMPUTE
+end
+
+if   type == PLAIN
+then puts ("0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21");
+end
+
+if   type == COMPUTE
+then for n in 1 .. COUNT
+         if n > 1
+         then print (", ")
+         end
+         print divisor_sum (n)
+     end
+     puts ("")
+end
diff --git a/challenge-109/abigail/scheme/ch-1.scm b/challenge-109/abigail/scheme/ch-1.scm
new file mode 100644
index 0000000000..bc43f3c502
--- /dev/null
+++ b/challenge-109/abigail/scheme/ch-1.scm
@@ -0,0 +1,9 @@
+;;;
+;;; See ../README.md
+;;;
+
+;;;
+;;; Run as: guile --no-auto-compile ch-1.scm
+;;;
+
+(display "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21\n")
diff --git a/challenge-109/abigail/sed/ch-1.sed b/challenge-109/abigail/sed/ch-1.sed
new file mode 100644
index 0000000000..1c93d3f21c
--- /dev/null
+++ b/challenge-109/abigail/sed/ch-1.sed
@@ -0,0 +1,12 @@
+#
+# See ../README.md
+#
+
+#
+# Run as: sed -f ch-1.sed
+#
+# For each line in the input file, we write the first three
+# self-describing numbers.
+#
+
+s/.*/0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21/
diff --git a/challenge-109/abigail/sql/ch-1.sql b/challenge-109/abigail/sql/ch-1.sql
new file mode 100644
index 0000000000..014860fcd5
--- /dev/null
+++ b/challenge-109/abigail/sql/ch-1.sql
@@ -0,0 +1,9 @@
+--
+-- See ../README.md
+--
+
+-- 
+-- Run as: sqlite3 < ch-1.sql
+--
+
+SELECT "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21";
diff --git a/challenge-109/abigail/t/ctest.ini b/challenge-109/abigail/t/ctest.ini
new file mode 100644
index 0000000000..e2f88e41ce
--- /dev/null
+++ b/challenge-109/abigail/t/ctest.ini
@@ -0,0 +1,35 @@
+# 
+# Configuration file for running tests, using ctest.
+# See https://github.com/Abigail/Misc/blob/master/ctest
+# 
+
+[names]
+1-1 = Fixed output
+1-2 = Fixed output/plain
+1-3 = Fixed output/fetch
+1-4 = Fixed output/compute
+
+
+[1-1]
+no_input = 1
+
+[1-1/sed]
+no_input = 0
+
+[1-1/awk,bash,c,lua,node,perl,python,ruby]
+skip = "Not for this language"
+
+[1-2,1-3,1-4]
+skip = "Not for this language"
+
+[1-2/awk,bash,c,lua,node,perl,python,ruby]
+skip = 0
+args = plain
+
+[1-3/perl]
+skip = 0
+args = fetch
+
+[1-4/awk,bash,c,lua,node,perl,python,ruby]
+skip = 0
+args = compute
diff --git a/challenge-109/abigail/t/input-1-1 b/challenge-109/abigail/t/input-1-1
new file mode 100644
index 0000000000..8b13789179
--- /dev/null
+++ b/challenge-109/abigail/t/input-1-1
@@ -0,0 +1 @@
+
diff --git a/challenge-109/abigail/t/input-1-2 b/challenge-109/abigail/t/input-1-2
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/challenge-109/abigail/t/input-1-3 b/challenge-109/abigail/t/input-1-3
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/challenge-109/abigail/t/input-1-4 b/challenge-109/abigail/t/input-1-4
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/challenge-109/abigail/t/output-1-1.exp b/challenge-109/abigail/t/output-1-1.exp
new file mode 100644
index 0000000000..9299e87f97
--- /dev/null
+++ b/challenge-109/abigail/t/output-1-1.exp
@@ -0,0 +1 @@
+0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21
diff --git a/challenge-109/abigail/t/output-1-2.exp b/challenge-109/abigail/t/output-1-2.exp
new file mode 100644
index 0000000000..9299e87f97
--- /dev/null
+++ b/challenge-109/abigail/t/output-1-2.exp
@@ -0,0 +1 @@
+0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21
diff --git a/challenge-109/abigail/t/output-1-3.exp b/challenge-109/abigail/t/output-1-3.exp
new file mode 100644
index 0000000000..9299e87f97
--- /dev/null
+++ b/challenge-109/abigail/t/output-1-3.exp
@@ -0,0 +1 @@
+0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21
diff --git a/challenge-109/abigail/t/output-1-4.exp b/challenge-109/abigail/t/output-1-4.exp
new file mode 100644
index 0000000000..9299e87f97
--- /dev/null
+++ b/challenge-109/abigail/t/output-1-4.exp
@@ -0,0 +1 @@
+0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21
diff --git a/challenge-109/abigail/tcl/ch-1.tcl b/challenge-109/abigail/tcl/ch-1.tcl
new file mode 100644
index 0000000000..7ab10d4661
--- /dev/null
+++ b/challenge-109/abigail/tcl/ch-1.tcl
@@ -0,0 +1,9 @@
+#
+# See ../README.md
+#
+
+#
+# Run as: tclsh ch-1.tcl
+#
+
+puts "0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21"
-- 
cgit 


From 5be6a97a3cf0ff10e023171729a50a386c24622b Mon Sep 17 00:00:00 2001
From: Abigail <abigail@abigail.be>
Date: Tue, 20 Apr 2021 18:24:30 +0200
Subject: Perl solution for week 109, part 2

---
 challenge-109/abigail/README.md        |   1 +
 challenge-109/abigail/perl/ch-2.pl     | 183 +++++++++++++++++++++++++++++++++
 challenge-109/abigail/t/ctest.ini      |   6 ++
 challenge-109/abigail/t/input-2-1      |   1 +
 challenge-109/abigail/t/input-2-2      |   1 +
 challenge-109/abigail/t/output-2-1.exp |   8 ++
 challenge-109/abigail/t/output-2-2.exp |   2 +
 7 files changed, 202 insertions(+)
 create mode 100644 challenge-109/abigail/perl/ch-2.pl
 create mode 100644 challenge-109/abigail/t/input-2-1
 create mode 100644 challenge-109/abigail/t/input-2-2
 create mode 100644 challenge-109/abigail/t/output-2-1.exp
 create mode 100644 challenge-109/abigail/t/output-2-2.exp

diff --git a/challenge-109/abigail/README.md b/challenge-109/abigail/README.md
index 57a25f7869..1f7b55f195 100644
--- a/challenge-109/abigail/README.md
+++ b/challenge-109/abigail/README.md
@@ -91,6 +91,7 @@ Output:
 ~~~~
 
 ### Solutions
+* [Perl](perl/ch-2.pl)
 
 ### Blog
 
diff --git a/challenge-109/abigail/perl/ch-2.pl b/challenge-109/abigail/perl/ch-2.pl
new file mode 100644
index 0000000000..ddbbe4fb38
--- /dev/null
+++ b/challenge-109/abigail/perl/ch-2.pl
@@ -0,0 +1,183 @@
+#!/opt/perl/bin/perl
+
+use 5.032;
+
+use strict;
+use warnings;
+no  warnings 'syntax';
+
+use experimental 'signatures';
+use experimental 'lexical_subs';
+
+#
+# See ../README.md
+#
+
+#
+# Run as: perl ch-2.pl < input-file
+#
+
+#
+# First note that due to symmetry, there cannot be a unique solution [1].
+# If
+#
+#      (a, b, c, d, e, f, g) = (x_1, x_2, x_3, x_4, x_5, x_6, x_7)
+#
+# is a solution, then
+#
+#      (a, b, c, d, e, f, g) = (x_7, x_6, x_5, x_4, x_3, x_2, x_1)
+#
+# must be a solution as well.
+#
+# For instance, the given example has 8 solutions, 4 of which are
+# mirror images.
+#
+# [1] This assumes no duplicate numbers in the input. Clearly, a
+#     solution where a == g, b == f, and c == e doesn't give a
+#     different solution when mirrorred. (For instance, if all 
+#     numbers are 0, there is only one solution).
+
+#
+#
+# It's easy to brute force this. There are a mere 5040 permutations
+# of the seven numbers; it would be hard to find an environment
+# where it takes more than a few milliseconds to try all permutations.
+#
+# We can improve the brute force a little, by determining early we're
+# on a wrong path. For instance, once we have picked an a, b, c, and d,
+# we can check whether a + b == b + c + d. If not, we don't have to
+# continue trying values for e, f, and g.
+#
+# However, that's not the way we go. We will first do some analysis.
+# Let the sum of each box be N. Then we have:
+#
+#   N = a + b        (1)
+#   N = b + c + d    (2)
+#   N = d + e + f    (3)
+#   N = f + g        (4)
+#
+# For (1) and (2), we get:
+#
+#   a + b = b + c + d  =>
+#   a     =     c + d  =>
+#   a - c =         d
+#
+# In the same way, (3) and (4), we get:
+#
+#   g + f = f + e + d  =>
+#   g     =     e + d  =>
+#   g - e =         d
+#
+# This leads to the following algorithm:
+# 
+#   - Calculate the differences between all pairs (7 * 6 == 42 pairs)
+#   - Find all numbers n from the input array for which there are at
+#     least two pairs giving this difference, under the condition n
+#     is not part of such a pair. (Note that if the input contains
+#     two or more of the same number, for this purpose, we treat those
+#     numbers to be different). These numbers will be our candidate for d.
+#   - Of the list of differences equalling d, consider each pair.
+#     Eliminate pairs where the same number appears in each. The first
+#     difference gives candidates for a and c; the second gives candidates
+#     for g and e. (Swapping them leaves to a symmetric solution).
+#   - We now have candidates for a, c, d, e, and g. This leaves two
+#     numbers for b and c.
+#   - Try both, and check whether a + b == b + c + d == d + e + f == f + g.
+#
+# For the given example, this means we only try 32 permutations,
+# giving us 4 different solutions (the other 4 can be found by
+# reversing the numbers).
+#
+# We are not making any assumptions on the sign of the input numbers;
+# our algorithm works fine if the input contains negative numbers.
+#
+# We will also print all solutions (including the symmetric ones)
+#
+
+while (<>) {
+    my @numbers = split;
+
+    #
+    # Find all differences
+    #
+    my %differences;
+    for (my $x = 0; $x < @numbers; $x ++) {
+        for (my $y = $x + 1; $y < @numbers; $y ++) {
+            my $diff = $numbers [$x] - $numbers [$y];
+            push @{$differences { $diff}} => [$x, $y];
+            push @{$differences {-$diff}} => [$y, $x];
+        }
+    }
+
+    #
+    # Now, iterate over the numbers, and see if there 
+    # is a number matching two differences, with all
+    # indices being different.
+    #
+    for (my $d_i = 0; $d_i < @numbers; $d_i ++) {
+        my $d = $numbers [$d_i];
+        #
+        # Find the pairs whose difference is $d. If we don't have
+        # at least two pairs where neither number is $d, this
+        # cannot be a solution.
+        #
+        my @diffs = grep {$$_ [0] != $d_i && $$_ [1] != $d_i}
+                          @{$differences {$d} || []};
+
+        next unless @diffs >= 2;
+
+        #
+        # Now, find two pairs where all indices are different.
+        #
+        for (my $x = 0; $x < @diffs; $x ++) {
+            for (my $y = $x + 1; $y < @diffs; $y ++) {
+                next if $diffs [$x] [0] == $diffs [$y] [0] ||
+                        $diffs [$x] [0] == $diffs [$y] [1] ||
+                        $diffs [$x] [1] == $diffs [$y] [0] ||
+                        $diffs [$x] [1] == $diffs [$y] [1];
+
+                #
+                # W.l.o.g. we can now assume $diffs [$x] are
+                # the indices for $a and $c, and $diffs [$y]
+                # are the indices for $g and $e.
+                #
+                my ($a_i, $c_i) = @{$diffs [$x]};
+                my ($g_i, $e_i) = @{$diffs [$y]};
+
+                #
+                # Find the unused indices
+                #
+                my %indices = map {$_ => 1} keys @numbers;
+                delete $indices {$_} for $a_i, $c_i, $d_i, $e_i, $g_i;
+
+                #
+                # This leaves two indices for $b and $e.
+                # Try them both.
+                #
+                my $left = [keys %indices];
+                foreach my $try ($left, [reverse @$left]) {
+                    my ($b_i, $f_i) = @$try;
+
+                    #
+                    # Do we have a winner?
+                    #
+                    next unless           $numbers [$a_i] + $numbers [$b_i] ==
+                        $numbers [$b_i] + $numbers [$c_i] + $numbers [$d_i] ==
+                        $numbers [$d_i] + $numbers [$e_i] + $numbers [$f_i] ==
+                                          $numbers [$f_i] + $numbers [$g_i];
+
+                    #
+                    # Print result, and the reverse, so we get all
+                    # possible solutions.
+                    #
+                    my @solution =
+                       @numbers [$a_i, $b_i, $c_i, $d_i, $e_i, $f_i, $g_i];
+
+                    local $, = " ";
+                    say         @solution;
+                    say reverse @solution;
+                }
+            }
+        }
+    }
+}
diff --git a/challenge-109/abigail/t/ctest.ini b/challenge-109/abigail/t/ctest.ini
index e2f88e41ce..afa82182bd 100644
--- a/challenge-109/abigail/t/ctest.ini
+++ b/challenge-109/abigail/t/ctest.ini
@@ -8,6 +8,8 @@
 1-2 = Fixed output/plain
 1-3 = Fixed output/fetch
 1-4 = Fixed output/compute
+2-1 = Given example
+2-2 = With a negative number
 
 
 [1-1]
@@ -33,3 +35,7 @@ args = fetch
 [1-4/awk,bash,c,lua,node,perl,python,ruby]
 skip = 0
 args = compute
+
+
+[2-1,2-2]
+sort = 1
diff --git a/challenge-109/abigail/t/input-2-1 b/challenge-109/abigail/t/input-2-1
new file mode 100644
index 0000000000..b4457aae66
--- /dev/null
+++ b/challenge-109/abigail/t/input-2-1
@@ -0,0 +1 @@
+1 2 3 4 5 6 7
diff --git a/challenge-109/abigail/t/input-2-2 b/challenge-109/abigail/t/input-2-2
new file mode 100644
index 0000000000..335e2405f0
--- /dev/null
+++ b/challenge-109/abigail/t/input-2-2
@@ -0,0 +1 @@
+1 -2 3 4 5 6 7
diff --git a/challenge-109/abigail/t/output-2-1.exp b/challenge-109/abigail/t/output-2-1.exp
new file mode 100644
index 0000000000..83687f2b3e
--- /dev/null
+++ b/challenge-109/abigail/t/output-2-1.exp
@@ -0,0 +1,8 @@
+3 7 2 1 5 4 6
+4 5 3 1 6 2 7
+4 7 1 3 2 6 5
+5 6 2 3 1 7 4
+6 4 1 5 2 3 7
+6 4 5 1 2 7 3
+7 2 6 1 3 5 4
+7 3 2 5 1 4 6
diff --git a/challenge-109/abigail/t/output-2-2.exp b/challenge-109/abigail/t/output-2-2.exp
new file mode 100644
index 0000000000..7a67a5be9d
--- /dev/null
+++ b/challenge-109/abigail/t/output-2-2.exp
@@ -0,0 +1,2 @@
+3 7 -2 5 1 4 6
+6 4 1 5 -2 7 3
-- 
cgit 


From 490b2215c7eaeb037b7548564306e2081784b3e4 Mon Sep 17 00:00:00 2001
From: Abigail <abigail@abigail.be>
Date: Tue, 20 Apr 2021 20:43:18 +0200
Subject: Use function argument

---
 challenge-109/abigail/bash/ch-1.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/challenge-109/abigail/bash/ch-1.sh b/challenge-109/abigail/bash/ch-1.sh
index d4eec1f2d9..de09aa6414 100644
--- a/challenge-109/abigail/bash/ch-1.sh
+++ b/challenge-109/abigail/bash/ch-1.sh
@@ -13,6 +13,7 @@ set -f
 COUNT=20
 
 function divisor_sum () {
+    local n=$1
     sum=0
     local i
     for ((i = 2; i < n; i ++))
-- 
cgit 


From 7b4fbbe6505b63d2faa62ad34939b6e830ea692b Mon Sep 17 00:00:00 2001
From: Abigail <abigail@abigail.be>
Date: Tue, 20 Apr 2021 20:52:57 +0200
Subject: When looping over possible divisors, stop at n / 2.

---
 challenge-109/abigail/awk/ch-1.awk   | 2 +-
 challenge-109/abigail/bash/ch-1.sh   | 2 +-
 challenge-109/abigail/c/ch-1.c       | 2 +-
 challenge-109/abigail/lua/ch-1.lua   | 2 +-
 challenge-109/abigail/node/ch-1.js   | 2 +-
 challenge-109/abigail/perl/ch-1.pl   | 2 +-
 challenge-109/abigail/python/ch-1.py | 2 +-
 challenge-109/abigail/ruby/ch-1.rb   | 2 +-
 8 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/challenge-109/abigail/awk/ch-1.awk b/challenge-109/abigail/awk/ch-1.awk
index 6b889ae3a0..203c7f1fec 100644
--- a/challenge-109/abigail/awk/ch-1.awk
+++ b/challenge-109/abigail/awk/ch-1.awk
@@ -10,7 +10,7 @@
 
 function divisor_sum (n, i) {
     sum = 0
-    for (i = 2; i < n; i ++) {
+    for (i = 2; i <= n / 2; i ++) {
         if (n % i == 0) {
             sum += i
         }
diff --git a/challenge-109/abigail/bash/ch-1.sh b/challenge-109/abigail/bash/ch-1.sh
index de09aa6414..752a4f9760 100644
--- a/challenge-109/abigail/bash/ch-1.sh
+++ b/challenge-109/abigail/bash/ch-1.sh
@@ -16,7 +16,7 @@ function divisor_sum () {
     local n=$1
     sum=0
     local i
-    for ((i = 2; i < n; i ++))
+    for ((i = 2; i <= n / 2; i ++))
     do  if   ((n % i == 0))
         then ((sum += i))
         fi
diff --git a/challenge-109/abigail/c/ch-1.c b/challenge-109/abigail/c/ch-1.c
index e6716c148a..377caf63f3 100644
--- a/challenge-109/abigail/c/ch-1.c
+++ b/challenge-109/abigail/c/ch-1.c
@@ -20,7 +20,7 @@ typedef int number;  /* Change if we want large numbers */
 
 number divisor_sum (number n) {
     number sum = 0;
-    for (number i = 2; i < n; i ++) {
+    for (number i = 2; i <= n / 2; i ++) {
         if (!(n % i)) {
             sum += i;
         }
diff --git a/challenge-109/abigail/lua/ch-1.lua b/challenge-109/abigail/lua/ch-1.lua
index 5eb2d477f9..74c3b7d914 100644
--- a/challenge-109/abigail/lua/ch-1.lua
+++ b/challenge-109/abigail/lua/ch-1.lua
@@ -15,7 +15,7 @@ local COUNT   = 20
 
 function divisor_sum (n)
     local sum = 0
-    for i = 2, n - 2 do
+    for i = 2, n / 2 do
         if   n % i == 0 
         then sum = sum + i
         end
diff --git a/challenge-109/abigail/node/ch-1.js b/challenge-109/abigail/node/ch-1.js
index d7cff7b0f5..0f75cf4962 100644
--- a/challenge-109/abigail/node/ch-1.js
+++ b/challenge-109/abigail/node/ch-1.js
@@ -15,7 +15,7 @@ let COUNT   = 20
 
 function divisor_sum (n) {
     let sum = 0
-    for (let i = 2; i < n; i ++) {
+    for (let i = 2; i <= Math . floor (n / 2); i ++) {
         if (n % i == 0) {
             sum += i
         }
diff --git a/challenge-109/abigail/perl/ch-1.pl b/challenge-109/abigail/perl/ch-1.pl
index 64f21d5d24..967a0344de 100644
--- a/challenge-109/abigail/perl/ch-1.pl
+++ b/challenge-109/abigail/perl/ch-1.pl
@@ -47,5 +47,5 @@ elsif ($type == $TYPE_COMPUTE) {
     # calculate the first 20 numbers, we don't have to care about
     # efficiency.
     #
-    say map {my $n = $_; sum0 grep {!($n % $_)} 2 .. $_ - 1} 1 .. $COUNT;
+    say map {my $n = $_; sum0 grep {!($n % $_)} 2 .. $_ / 2} 1 .. $COUNT;
 }
diff --git a/challenge-109/abigail/python/ch-1.py b/challenge-109/abigail/python/ch-1.py
index 6600bda6d5..f9e51a0897 100644
--- a/challenge-109/abigail/python/ch-1.py
+++ b/challenge-109/abigail/python/ch-1.py
@@ -16,7 +16,7 @@ COMPUTE =  1
 
 def divisor_sum (n):
     sum = 0
-    for i in range (2, n):
+    for i in range (2, n / 2 + 1):
         if n % i == 0:
             sum = sum + i
     return (sum)
diff --git a/challenge-109/abigail/ruby/ch-1.rb b/challenge-109/abigail/ruby/ch-1.rb
index 95a38a69cb..0c73c368dd 100644
--- a/challenge-109/abigail/ruby/ch-1.rb
+++ b/challenge-109/abigail/ruby/ch-1.rb
@@ -15,7 +15,7 @@ COUNT   = 20
 
 def divisor_sum (n)
     sum = 0
-    for i in 2 .. n - 1
+    for i in 2 .. n / 2
         if   n % i == 0
         then sum += i
         end
-- 
cgit 


From fff9e4703ed20a60640c4ef24219499eb532ecb3 Mon Sep 17 00:00:00 2001
From: Lance Wicks <lw@judocoach.com>
Date: Wed, 21 Apr 2021 20:21:20 +0100
Subject: Perl implementation for 108, thanks Mohammad!

---
 challenge-109/lance-wicks/perl/ch-1.pl       | 12 ++++++++++++
 challenge-109/lance-wicks/perl/lib/Chowla.pm | 26 ++++++++++++++++++++++++++
 challenge-109/lance-wicks/perl/t/01-chowla.t | 12 ++++++++++++
 3 files changed, 50 insertions(+)
 create mode 100644 challenge-109/lance-wicks/perl/ch-1.pl
 create mode 100644 challenge-109/lance-wicks/perl/lib/Chowla.pm
 create mode 100644 challenge-109/lance-wicks/perl/t/01-chowla.t

diff --git a/challenge-109/lance-wicks/perl/ch-1.pl b/challenge-109/lance-wicks/perl/ch-1.pl
new file mode 100644
index 0000000000..ddbb11ad8a
--- /dev/null
+++ b/challenge-109/lance-wicks/perl/ch-1.pl
@@ -0,0 +1,12 @@
+use strict;
+use warnings;
+
+use lib './lib';
+use Chowla;
+
+my $c = Chowla->new;
+my $numbers = $c->list(20);
+
+for my $n (@$numbers) {
+    print "$n, ";
+}
diff --git a/challenge-109/lance-wicks/perl/lib/Chowla.pm b/challenge-109/lance-wicks/perl/lib/Chowla.pm
new file mode 100644
index 0000000000..06619c38d2
--- /dev/null
+++ b/challenge-109/lance-wicks/perl/lib/Chowla.pm
@@ -0,0 +1,26 @@
+package Chowla;
+
+use Moo;
+
+sub list {
+    my ($self,$max) = @_;
+    my @chowla_numbers;
+    for my $n (1..$max) {
+        push @chowla_numbers, $self->n($n);
+    }
+    return \@chowla_numbers;
+}
+
+sub n {
+    my ($self,$num) = @_;
+
+    my $total = 0;
+    for my $n (2..$num-1) {
+        if ($num % $n == 0) {
+            $total += $n;
+        }
+    }
+    return $total;
+}
+
+1;
diff --git a/challenge-109/lance-wicks/perl/t/01-chowla.t b/challenge-109/lance-wicks/perl/t/01-chowla.t
new file mode 100644
index 0000000000..15d50ac14e
--- /dev/null
+++ b/challenge-109/lance-wicks/perl/t/01-chowla.t
@@ -0,0 +1,12 @@
+use Test2::V0 -target => 'Chowla';
+
+is $CLASS->list(20),[0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21], 'List the first 20 Chowla numbers';
+
+is $CLASS->n(1),0, 'First Chowla number should be zero';
+is $CLASS->n(2),0, 'Second Chowla number should be zero';
+is $CLASS->n(3),0, 'Third Chowla number should be zero';
+is $CLASS->n(4),2, 'Fourth Chowla number should be two';
+is $CLASS->n(5),0, 'Fifth Chowla number should be 0';
+is $CLASS->n(6),5, 'Sixth Chowla number should be 5';
+
+done_testing;
-- 
cgit 


From 97ed1c6391ff0077df0c446603be46db1e6bf219 Mon Sep 17 00:00:00 2001
From: Adam Russell <russella3@wit.edu>
Date: Wed, 21 Apr 2021 19:51:47 -0400
Subject: initial commit

---
 challenge-109/adam-russell/blog.txt      | 0
 challenge-109/adam-russell/blog1.txt     | 0
 challenge-109/adam-russell/perl/ch-1.pl  | 0
 challenge-109/adam-russell/perl/ch-2.pl  | 0
 challenge-109/adam-russell/prolog/ch-1.p | 0
 challenge-109/adam-russell/prolog/ch-2.p | 0
 6 files changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 challenge-109/adam-russell/blog.txt
 create mode 100644 challenge-109/adam-russell/blog1.txt
 create mode 100644 challenge-109/adam-russell/perl/ch-1.pl
 create mode 100644 challenge-109/adam-russell/perl/ch-2.pl
 create mode 100644 challenge-109/adam-russell/prolog/ch-1.p
 create mode 100644 challenge-109/adam-russell/prolog/ch-2.p

diff --git a/challenge-109/adam-russell/blog.txt b/challenge-109/adam-russell/blog.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/challenge-109/adam-russell/blog1.txt b/challenge-109/adam-russell/blog1.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/challenge-109/adam-russell/perl/ch-1.pl b/challenge-109/adam-russell/perl/ch-1.pl
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/challenge-109/adam-russell/perl/ch-2.pl b/challenge-109/adam-russell/perl/ch-2.pl
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/challenge-109/adam-russell/prolog/ch-1.p b/challenge-109/adam-russell/prolog/ch-1.p
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/challenge-109/adam-russell/prolog/ch-2.p b/challenge-109/adam-russell/prolog/ch-2.p
new file mode 100644
index 0000000000..e69de29bb2
-- 
cgit 


From afa7e43f4969e15ad2b07540e4fadf8e72b691dc Mon Sep 17 00:00:00 2001
From: Abigail <abigail@abigail.be>
Date: Thu, 22 Apr 2021 14:58:53 +0200
Subject: AWK solution for week 109. part 2

---
 challenge-109/abigail/README.md    |   1 +
 challenge-109/abigail/awk/ch-2.awk | 126 +++++++++++++++++++++++++++++++++++++
 2 files changed, 127 insertions(+)
 create mode 100644 challenge-109/abigail/awk/ch-2.awk

diff --git a/challenge-109/abigail/README.md b/challenge-109/abigail/README.md
index 1f7b55f195..3928e7302c 100644
--- a/challenge-109/abigail/README.md
+++ b/challenge-109/abigail/README.md
@@ -91,6 +91,7 @@ Output:
 ~~~~
 
 ### Solutions
+* [AWK](awk/ch-2.awk)
 * [Perl](perl/ch-2.pl)
 
 ### Blog
diff --git a/challenge-109/abigail/awk/ch-2.awk b/challenge-109/abigail/awk/ch-2.awk
new file mode 100644
index 0000000000..9476ec90e8
--- /dev/null
+++ b/challenge-109/abigail/awk/ch-2.awk
@@ -0,0 +1,126 @@
+#!/usr/bin/awk
+
+#
+# See ../README.md
+#
+
+#
+# Run as: awk -f ch-2.awk < input-file
+#
+
+{
+    SIZE = 7;
+    #
+    # Put the fields into an array.
+    #
+    for (i = 1; i <= SIZE; i ++) {
+        numbers [i] = $i
+    }
+
+    #
+    # Find all the differences between pairs of numbers
+    #
+    delete diffs
+    delete diff_count
+    for (i = 1; i <= SIZE; i ++) {
+        for (j = i + 1; j <= SIZE; j ++) {
+            diff = numbers [i] - numbers [j]
+            diff_count [ diff] ++
+            diff_count [-diff] ++
+            l1 = diff_count [ diff]
+            l2 = diff_count [-diff]
+            diffs [ diff, l1, 1] = i
+            diffs [ diff, l1, 2] = j
+            diffs [-diff, l2, 1] = j
+            diffs [-diff, l2, 2] = i
+        }
+    }
+
+    #
+    # Iterate over the numbers, and see if there is a number
+    # which is equal to at least two differences.
+    #
+    # These numbers will be possibilities for d (at index d_i)
+    #
+    for (d_i = 1; d_i <= SIZE; d_i ++) {
+        d = numbers [d_i]
+        c = diff_count [d]
+        if (diff_count [d] >= 2) {
+            #
+            # Find two pairs whose difference is d, where none
+            # of the five numbers is reused.
+            #
+            for (i = 1; i <= c; i ++) {
+                if (diffs [d, i, 1] != d_i && diffs [d, i, 2] != d_i) {
+                    for (j = i + 1; j <= c; j ++) {
+                        if (diffs [d, j, 1] != d_i &&
+                            diffs [d, j, 2] != d_i &&
+                            diffs [d, i, 1] != diffs [d, j, 1] &&
+                            diffs [d, i, 1] != diffs [d, j, 2] &&
+                            diffs [d, i, 2] != diffs [d, j, 1] &&
+                            diffs [d, i, 2] != diffs [d, j, 2]) {
+                            #
+                            # W.l.o.g we can now assume diffs [d, i]
+                            # contains the indices for a and c,
+                            # and diffs [d, j] the indices for g and e.
+                            #
+                            a_i = diffs [d, i, 1]
+                            c_i = diffs [d, i, 2]
+                            g_i = diffs [d, j, 1]
+                            e_i = diffs [d, j, 2]
+
+                            #
+                            # Find the unused positions for b and f
+                            #
+                            for (b_i = 1; b_i <= SIZE; b_i ++) {
+                                if (b_i != a_i && b_i != c_i && b_i != d_i &&
+                                    b_i != e_i && b_i != g_i) {
+                                    for (f_i = 1; f_i <= SIZE; f_i ++) {
+                                        if (f_i != a_i && f_i != b_i &&
+                                            f_i != c_i && f_i != d_i &&
+                                            f_i != e_i && f_i != g_i) {
+                                            #
+                                            # Do we have a winner?
+                                            #
+                                            target = numbers [a_i] + \
+                                                     numbers [b_i]
+                                            if (target == numbers [b_i] + \
+                                                          numbers [c_i] +  \
+                                                          numbers [d_i] &&
+                                                target == numbers [d_i] + \
+                                                          numbers [e_i] + \
+                                                          numbers [f_i] &&
+                                                target == numbers [f_i] + \
+                                                          numbers [g_i]) {
+                                                #
+                                                # We have a winner. Print
+                                                # it, and the reverse
+                                                #
+                                                printf "%d %d %d %d %d %d %d\n",
+                                                       numbers [a_i],
+                                                       numbers [b_i],
+                                                       numbers [c_i],
+                                                       numbers [d_i],
+                                                       numbers [e_i],
+                                                       numbers [f_i],
+                                                       numbers [g_i]
+                                                printf "%d %d %d %d %d %d %d\n",
+                                                       numbers [g_i],
+                                                       numbers [f_i],
+                                                       numbers [e_i],
+                                                       numbers [d_i],
+                                                       numbers [c_i],
+                                                       numbers [b_i],
+                                                       numbers [a_i]
+                                            }
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
-- 
cgit 


From 105b08ecd006e8f7e5e6b23c2d4b15ab0e449725 Mon Sep 17 00:00:00 2001
From: Abigail <abigail@abigail.be>
Date: Thu, 22 Apr 2021 20:02:42 +0200
Subject: C solution for week 109, part 2

---
 challenge-109/abigail/README.md |  2 +
 challenge-109/abigail/c/ch-2.c  | 87 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 89 insertions(+)
 create mode 100644 challenge-109/abigail/c/ch-2.c

diff --git a/challenge-109/abigail/README.md b/challenge-109/abigail/README.md
index 3928e7302c..815fe7fd8e 100644
--- a/challenge-109/abigail/README.md
+++ b/challenge-109/abigail/README.md
@@ -92,6 +92,8 @@ Output:
 
 ### Solutions
 * [AWK](awk/ch-2.awk)
+* [Bash](bash/ch-2.sh)
+* [C](c/ch-2.c)
 * [Perl](perl/ch-2.pl)
 
 ### Blog
diff --git a/challenge-109/abigail/c/ch-2.c b/challenge-109/abigail/c/ch-2.c
new file mode 100644
index 0000000000..19d95ad9f5
--- /dev/null
+++ b/challenge-109/abigail/c/ch-2.c
@@ -0,0 +1,87 @@
+# include <stdlib.h>
+# include <stdio.h>
+# include <string.h>
+
+/*
+ * See ../README.md
+ */
+
+/*
+ * Run as: cc -o ch-2.o ch-2.c; ./ch-2.o < input-file
+ */
+
+# define SIZE 7
+typedef int number;
+
+int main (void) {
+    number * numbers;
+    char *  line    = NULL;
+    size_t  len     = 0;
+
+    if ((numbers = (number *) malloc (SIZE * sizeof (number))) == NULL) {
+        perror ("Malloc numbers failed");
+        exit (1);
+    }
+
+    while (getline (&line, &len, stdin) != -1) {
+        if (sscanf (line, "%d %d %d %d %d %d %d",      &numbers [0],
+                           &numbers [1], &numbers [2], &numbers [3],
+                           &numbers [4], &numbers [5], &numbers [6]) != SIZE) {
+            continue;
+        }
+
+        for (size_t a_i = 0; a_i < SIZE; a_i ++) {
+            for (size_t b_i = 0; b_i < SIZE; b_i ++) {
+                if (a_i == b_i) {
+                    continue;
+                }
+                number target = numbers [a_i] + numbers [b_i];
+                for (size_t c_i = 0; c_i < SIZE; c_i ++) {
+                    if (a_i == c_i || b_i == c_i) {
+                        continue;
+                    }
+                    for (size_t d_i = 0; d_i < SIZE; d_i ++) {
+                        if (a_i == d_i || b_i == d_i || c_i == d_i ||
+                            target != numbers [b_i] + numbers [c_i] +
+                                      numbers [d_i]) {
+                            continue;
+                        }
+                        for (size_t e_i = 0; e_i < SIZE; e_i ++) {
+                            if (a_i == e_i || b_i == e_i ||
+                                c_i == e_i || d_i == e_i) {
+                                continue;
+                            }
+                            for (size_t f_i = 0; f_i < SIZE; f_i ++) {
+                                if (a_i == f_i || b_i == f_i ||
+                                    c_i == f_i || d_i == f_i ||
+                                    e_i == f_i ||
+                                    target != numbers [d_i] + numbers [e_i] +
+                                              numbers [f_i]) {
+                                    continue;
+                                }
+                                for (size_t g_i = 0; g_i < SIZE; g_i ++) {
+                                    if (a_i == g_i || b_i == g_i ||
+                                        c_i == g_i || d_i == g_i ||
+                                        e_i == g_i || f_i == g_i ||
+                                        target != numbers [f_i] +
+                                                  numbers [g_i]) {
+                                        continue;
+                                    }
+                                    printf ("%d %d %d %d %d %d %d\n",
+                                              numbers [a_i], numbers [b_i],
+                                              numbers [c_i], numbers [d_i],
+                                              numbers [e_i], numbers [f_i],
+                                              numbers [g_i]);
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    free (line);
+
+    return (0);
+}
-- 
cgit 


From c08186dfa8428ca980a8c66f71731a06aa47a3f0 Mon Sep 17 00:00:00 2001
From: Adam Russell <russella3@wit.edu>
Date: Fri, 23 Apr 2021 10:49:09 -0400
Subject: Perl and Prolog solutions

---
 challenge-109/adam-russell/perl/ch-1.pl  | 29 ++++++++++++++
 challenge-109/adam-russell/perl/ch-2.pl  | 61 +++++++++++++++++++++++++++++
 challenge-109/adam-russell/prolog/ch-1.p | 42 ++++++++++++++++++++
 challenge-109/adam-russell/prolog/ch-2.p | 66 ++++++++++++++++++++++++++++++++
 4 files changed, 198 insertions(+)

diff --git a/challenge-109/adam-russell/perl/ch-1.pl b/challenge-109/adam-russell/perl/ch-1.pl
index e69de29bb2..e5b82ec61f 100644
--- a/challenge-109/adam-russell/perl/ch-1.pl
+++ b/challenge-109/adam-russell/perl/ch-1.pl
@@ -0,0 +1,29 @@
+use strict;
+use warnings;
+##
+# Write a script to generate first 20 Chowla Numbers.
+# C(n) = sum of divisors of n except 1 and n
+##
+use constant CHOWLA_COUNT => 20;
+sub factor{
+    my($n) = @_;
+    my @factors = ();
+    foreach my $j (2..sqrt($n)){
+        push @factors, $j if $n % $j == 0;
+        push @factors, ($n / $j) if $n % $j == 0 && $j ** 2 != $n;
+    }    
+    return @factors;  
+}
+
+sub chowla{
+    my(@factors) = @_;
+    my $sum = unpack("%32I*", pack("I*", @factors)); 
+}
+
+MAIN:{
+    my @chowla_numbers;
+    for my $n (1 .. CHOWLA_COUNT){
+        push @chowla_numbers, chowla(factor($n));
+    }
+    print join(", ", @chowla_numbers) . "\n"; 
+}
\ No newline at end of file
diff --git a/challenge-109/adam-russell/perl/ch-2.pl b/challenge-109/adam-russell/perl/ch-2.pl
index e69de29bb2..3278d340e3 100644
--- a/challenge-109/adam-russell/perl/ch-2.pl
+++ b/challenge-109/adam-russell/perl/ch-2.pl
@@ -0,0 +1,61 @@
+use strict;
+use warnings;
+##
+# You are given four squares as below with numbers named a,b,c,d,e,f,g.
+# to place the given unique numbers in the square box so that sum of 
+# numbers in each box is the same. 
+#               (1)                    (3)
+#        +--------------+      +--------------+
+#        �              �      �              �
+#        �      a       �      �      e       �
+#        �              � (2)  �              �  (4)
+#        �          +---+------+---+      +---+---------+
+#        �          �   �      �   �      �   �         �
+#        �          � b �      � d �      � f �         �
+#        �          �   �      �   �      �   �         �
+#        �          �   �      �   �      �   �         �
+#        +----------+---+      +---+------+---+         �
+#                   �       c      �      �      g      �
+#                   �              �      �             �
+#                   �              �      �             �
+#                   +--------------+      +-------------+
+##
+use AI::Prolog;
+
+my $prolog = do{
+    local $/;
+    <DATA>;
+}; 
+$prolog = new AI::Prolog($prolog); 
+$prolog->query("sums_in_squares([1,2,3,4,5,6,7], Squares).");
+
+my $result;
+while ($result = $prolog->results()){
+    print join(",", @{$result->[2]}) . "\n";
+}
+
+__DATA__
+member(X,[X|T]).
+member(X,[H|T]):- member(X,T).
+sums_in_squares(Numbers, [A, B, C, D, E, F, G]):-  
+    member(A, Numbers), 
+    member(B, Numbers),
+    member(C, Numbers),
+    member(D, Numbers),
+    member(E, Numbers),
+    member(F, Numbers),
+    member(G, Numbers),
+    A \= B, A \= C, A \= D, A \= E, A \= F, A \= G,
+    B \= A, B \= C, B \= D, B \= E, B \= F, B \= G,
+    C \= A, C \= B, C \= D, C \= E, C \= F, C \= G,
+    D \= A, D \= B, D \= C, D \= E, D \= F, D \= G,
+    E \= A, E \= B, E \= C, E \= D, E \= F, E \= G,
+    F \= A, F \= B, F \= C, F \= D, F \= E, F \= G,
+    G \= A, G \= B, G \= C, G \= D, G \= E, G \= F,
+    Box1 is A + B,
+    Box2 is B + C + D,
+    Box3 is D + E + F,
+    Box4 is F + G,
+    Box1 == Box2,
+    Box2 == Box3,
+    Box3 == Box4.
\ No newline at end of file
diff --git a/challenge-109/adam-russell/prolog/ch-1.p b/challenge-109/adam-russell/prolog/ch-1.p
index e69de29bb2..3e2458293b 100644
--- a/challenge-109/adam-russell/prolog/ch-1.p
+++ b/challenge-109/adam-russell/prolog/ch-1.p
@@ -0,0 +1,42 @@
+/*
+ Write a script to generate first 20 Chowla Numbers.
+ C(n) = sum of divisors of n except 1 and n
+*/
+
+:-initialization(main).
+
+print_with_comma([H|[]]):-
+    write(H), nl.
+print_with_comma([H|T]):-
+    write(H),
+    write(', '),
+    print_with_comma(T).
+
+factor(N, Factors):-
+    S is round(sqrt(N)),
+    fd_domain(X, 2, S),
+    R #= N rem X,
+    R #= 0,
+    Q #= N // X,
+    Q #\= X,
+    fd_labeling([Q, X]),
+    Factors = [Q, X].
+factor(N, Factors):-
+    S is round(sqrt(N)),
+    fd_domain(X, 2, S),
+    R #= N rem X,
+    R #= 0,
+    Q #= N // X,
+    Q #= X,
+    fd_labeling([Q]),
+    Factors = [Q].    
+
+chowla(ChowlaNumber):-
+    between(1, 20, N),
+    findall(F, factor(N, F), Fs), 
+    flatten(Fs, Factors),
+    sum_list(Factors, ChowlaNumber).
+
+main:-
+    findall(ChowlaNumber, chowla(ChowlaNumber), ChowlaNumbers),
+    print_with_comma(ChowlaNumbers).
\ No newline at end of file
diff --git a/challenge-109/adam-russell/prolog/ch-2.p b/challenge-109/adam-russell/prolog/ch-2.p
index e69de29bb2..f56e7aa1a9 100644
--- a/challenge-109/adam-russell/prolog/ch-2.p
+++ b/challenge-109/adam-russell/prolog/ch-2.p
@@ -0,0 +1,66 @@
+/*
+ You are given four squares as below with numbers named a,b,c,d,e,f,g.
+ to place the given unique numbers in the square box so that sum of 
+ numbers in each box is the same. 
+               (1)                    (3)
+        +--------------+      +--------------+
+        �              �      �              �
+        �      a       �      �      e       �
+        �              � (2)  �              �  (4)
+        �          +---+------+---+      +---+---------+
+        �          �   �      �   �      �   �         �
+        �          � b �      � d �      � f �         �
+        �          �   �      �   �      �   �         �
+        �          �   �      �   �      �   �         �
+        +----------+---+      +---+------+---+         �
+                   �       c      �      �      g      �
+                   �              �      �             �
+                   �              �      �             �
+                   +--------------+      +-------------+
+*/
+
+:-initialization(main).
+
+all_unique(_, []).
+all_unique(L, [V|T]) :-
+    fd_exactly(1, L, V),
+    all_unique(L, T).
+
+sums_in_squares_naive(Numbers, [A, B, C, D, E, F, G]):-  
+    member(A, Numbers), 
+    member(B, Numbers),
+    member(C, Numbers),
+    member(D, Numbers),
+    member(E, Numbers),
+    member(F, Numbers),
+    member(G, Numbers),
+    \+ (A == B; A == C; A == D; A == E; A == F; A == G),
+    \+ (B == A; B == C; B == D; B == E; B == F; B == G),
+    \+ (C == A; C == B; C == D; C == E; C == F; C == G),
+    \+ (D == A; D == B; D == C; D == E; D == F; D == G),
+    \+ (E == A; E == B; E == C; E == D; E == F; E == G),
+    \+ (F == A; F == B; F == C; F == D; F == E; F == G),
+    \+ (G == A; G == B; G == C; G == D; G == E; G == F),
+    Box1 is A + B,
+    Box2 is B + C + D,
+    Box3 is D + E + F,
+    Box4 is F + G,
+    Box1 == Box2,
+    Box2 == Box3,
+    Box3 == Box4.
+
+sums_in_squa