I don't know who to attribute this solution to, (I started to include the name of the author in later snippets), but it runs very fast.

#!/usr/bin/perl
use strict;
use warnings;

my @factors = prime_factors( shift );

print $_, $/ for @factors;

sub prime_factors {
    my $x = shift;
    my @factors;
    for ( my $y = 2; $y <= $x; $y++ ) {
        next if $x % $y;
        $x /= $y;
        push @factors, $y;
        redo;
    }
    return @factors;
}
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