Solution to task 1

1 files changed, 49 insertions, 0 deletions

diff --git a/challenge-109/jo-37/perl/ch-1.pl b/challenge-109/jo-37/perl/ch-1.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use Math::Prime::Util 'divisor_sum';
+use experimental 'signatures';
+
+our $examples;
+
+run_tests() if $examples;	# does not return
+
+die <<EOS unless @ARGV == 1;
+usage: $0 [-examples] [n]
+
+-examples
+    run the examples from the challenge
+ 
+n
+    print the first n Chowla numbers
+
+EOS
+
+
+### Input and Output
+
+say join ', ', map chowla($_), 1 .. $ARGV[0];
+
+
+### Implementation
+
+# Return the n-th Chowla number as the sum of n's nontrivial divisors.
+# The trivial divisors are 1 and n, which need to be subtracted from the
+# sum of all divisors.  For n = 1 these two numbers coincide and thus
+# only one subtrahend shall be applied.
+sub chowla ($n) {
+    divisor_sum($n) - $n - ($n > 1);
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    my $n;
+    is chowla(++$n), $_, "chowla($n) = $_" for
+        (0, 0, 0, 2, 0, 5, 0, 6, 3, 7, 0, 15, 0, 9, 8, 14, 0, 20, 0, 21);
+
+    done_testing;
+    exit;
+}