#!env perl
#
# factor.pl <Number>
#
# Print the list of prime factors for Number
#
# 20130206 Can't find a copy on my hard drive, so making it again
use strict;
use warnings;

my $num = shift or die "Expected number to factor!";
print "$num: ", join(", ", factors($num)), "\n";

sub factors {
    my $val=shift;
    return unless $val;

    my @primes = (1);
    if ($val < 0) {
        unshift @primes, -1;
        $val = -$val;
    }

    while ($val % 2 == 0) {
        push @primes, 2;
        $val = $val/2;
    }
    my $fac=3;
    while ($fac*$fac <= $val) {
        while ($val % $fac == 0) {
            push @primes, $fac;
            $val = $val / $fac;
        }
        $fac += 2;
    }
    push @primes, $val if $val > 1;
    return @primes;
}