> I'm attaching a slightly commented versionin case it helps
Forgot the attachment, sorry.
#!/usr/bin/env perl
use strict;
use warnings;
use feature 'say';
use POSIX 'floor'; #I don't want pdl's floor, to avoid confusing 'sequence'
use PDL::Lite;
use PDL::NiceSlice;
my $num=$ARGV[0];
my $max=floor(sqrt($num));
my $possible=PDL->sequence($max+1); #possible divisors<=sqrt($num)
$possible->((1)).=0; #1 is not prime
foreach(2..$max/2) { # eratosthenes sieve
next unless $possible->(($_)); #skip non primes
$possible->(2*$_:-1:$_).=0; # $_ is prime. Other multiples of $_
# are not; zero them out.
}
my $primes=$possible->where($possible); # non zero elements are prime
my $factors;
my $allfactors=PDL->zeros(0);
my $n=$num; # $n starts as number being factored
do {
$factors=$primes->where($n%$primes==0); #factors divide $n
$n/=$factors->prod; # $n is another factor: 1 or prime or composite
$allfactors=$allfactors->append($factors); #accumulate prime factors
} while $factors->nelem; #until no more factors found
# At this point either $num has been fully factored and $n==1 or $n is
# (the only) prime factor larger than sqrt($num) (this fails in my
# system for very large numbers for unknown reasons)
$allfactors=$allfactors->append($n) unless $n==1; #append it if not trivial
say $allfactors->qsort; # print result in increasing order
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