From f5f9c8a7c5b5e6e640c6e52579878e0ed5cc97fa Mon Sep 17 00:00:00 2001
From: Dave Jacoby <jacoby.david@gmail.com>
Date: Mon, 10 Jan 2022 19:44:04 -0500
Subject: 147 - 3 * 7 * 7

---
 challenge-147/dave-jacoby/perl/ch-1.pl | 35 ++++++++++++++++++++++++++++++++
 challenge-147/dave-jacoby/perl/ch-2.pl | 37 ++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)
 create mode 100644 challenge-147/dave-jacoby/perl/ch-1.pl
 create mode 100644 challenge-147/dave-jacoby/perl/ch-2.pl

diff --git a/challenge-147/dave-jacoby/perl/ch-1.pl b/challenge-147/dave-jacoby/perl/ch-1.pl
new file mode 100644
index 0000000000..edc998ee77
--- /dev/null
+++ b/challenge-147/dave-jacoby/perl/ch-1.pl
@@ -0,0 +1,35 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ say postderef signatures state };
+no warnings qw{ experimental };
+
+my %primes;
+my %trunc;
+my $c = 1;
+my $n = 2;
+
+while (1) {
+    if ( is_prime($n) ) {
+        $primes{$n}++;
+        my $copy = $n;
+        while ( length $copy > 0 ) {
+            last unless $primes{$copy};
+            substr( $copy, 0, 1 ) = '';
+            if ( $copy eq '' ) {
+                $trunc{$n}++ if $copy eq '';
+                last;
+            }
+        }
+        last if scalar keys %trunc > 20;
+    }
+    $n++;
+}
+
+say join ', ', sort { $a <=> $b } keys %trunc;
+
+sub is_prime ($n) {
+    for ( 2 .. sqrt $n ) { return unless $n % $_ }
+    return 1;
+}
diff --git a/challenge-147/dave-jacoby/perl/ch-2.pl b/challenge-147/dave-jacoby/perl/ch-2.pl
new file mode 100644
index 0000000000..4385f57450
--- /dev/null
+++ b/challenge-147/dave-jacoby/perl/ch-2.pl
@@ -0,0 +1,37 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+use feature qw{ say postderef signatures state };
+no warnings qw{ experimental };
+
+my $top      = 100_000;
+my @pentagon = map { pentagon($_) } 0 .. $top;
+my %pentagon = map { $_ => 1 } @pentagon;
+
+for my $i ( 1 .. $top ) {
+    for my $j ( 1 .. $i - 1 ) {
+        my $pi  = $pentagon[$i];
+        my $pj  = $pentagon[$j];
+        my $sum = $pi + $pj;
+
+        if ( $pentagon{$sum} ) {
+            my $product = abs( $pi - $pj );
+            if ( $pentagon{$product} ) {
+                say <<"END";
+        P($i) = $pi
+        P($j) = $pj
+        $pi + $pj = $sum
+        abs( $pi - $pj ) = $product
+END
+                exit;
+
+            }
+        }
+
+    }
+}
+
+sub pentagon ( $n ) {
+    return $n * ( ( $n * 3 ) - 1 ) / 2;
+}
-- 
cgit