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#!/usr/bin/env perl
use strict;
use warnings;
use feature qw'say state signatures';
no warnings qw'experimental::signatures';
run() unless caller();
sub run() {
say join( ', ', cuban_primes() );
}
sub cuban_primes($max = 1000) {
my @cubans = ();
my $i = 1;
my $candidate = 0;
while ( $candidate <= $max ) {
$candidate = centered_hexagonal_number($i);
push @cubans, $candidate if is_prime($candidate);
$i += 1;
}
return @cubans;
}
# from challenge 150 task 2
sub is_prime($x) {
return 0 if $x <= 1;
return 1 if $x <= 3;
for ( my $i = 2 ; $i <= sqrt($x) ; $i++ ) {
return 0 if $x % $i == 0;
}
return 1;
}
sub centered_hexagonal_number($y) {
return 3 * $y * $y + 3 * $y + 1;
}
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