foreach my $n ( @ARGV ? @ARGV : (20, 48, 96, 7, 69, 33, 13195,  600851475143, 2147483647) ) {

##</code><code>##

perl pm1194192.pl 18 54 27000 29474100
Number: 18 , Prime_Factors: => 2 3 3
Number: 54 , Prime_Factors: => 2 3 9
Number: 27000 , Prime_Factors: => 2 2 2 3 5 9 25
Number: 29474100 , Prime_Factors: => 2 2 3 5 15 32749
##</code><code>##

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

my $doSqrt; if($ARGV[0] eq '--sqrt') {$doSqrt = shift @ARGV;}   # added to toggle whether or not I do the sqrt after ever num

sub prime_factors {
    my $num = shift;
    my @primes = ();
    my $max = sqrt($num);
    while ($num % 2 == 0) {
        push @primes, 2;
        $num /= 2;
    }

    foreach (my $i = 3; $i <= $max; $i += 2) {
        if ($num % $i == 0) {
            push @primes, $i;
            $num /= $i;
            $max = sqrt($num) if $doSqrt;  # added by [pryrt]
            redo;               # changed from [id://1194102], where it used to be:     next;
        }
     }

     if ($num > 2) {
        push @primes, $num;
     }

     return @primes;
}

foreach my $n ( @ARGV ? @ARGV : (20, 48, 96, 7, 69, 33, 13195,  600851475143, 2147483647) ) {
    my @result = prime_factors($n);
    print "Number: $n , Prime_Factors: => @result", "\n";
}


##</code><code>##

$ time perl pm1194192.pl 18 54 27000 29474100 3217491003
Number: 18 , Prime_Factors: => 2 3 3
Number: 54 , Prime_Factors: => 2 3 3 3
Number: 27000 , Prime_Factors: => 2 2 2 3 3 3 5 5 5
Number: 29474100 , Prime_Factors: => 2 2 3 3 5 5 32749
Number: 3217491003 , Prime_Factors: => 3 32749 32749

real	0m0.010s
user	0m0.008s
sys	0m0.000s

$ time perl pm1194192.pl --sqrt 18 54 27000 29474100 3217491003
Number: 18 , Prime_Factors: => 2 3 3
Number: 54 , Prime_Factors: => 2 3 3 3
Number: 27000 , Prime_Factors: => 2 2 2 3 3 3 5 5 5
Number: 29474100 , Prime_Factors: => 2 2 3 3 5 5 32749
Number: 3217491003 , Prime_Factors: => 3 32749 32749

real	0m0.008s
user	0m0.004s
sys	0m0.000s

##</code><code>##

...
my @list = (20, 48, 96, 7, 69, 33, 13195,  600851475143, 2147483647, 18, 54, 27000, 29474100, 589806);
foreach my $n ( @list ) {
    my @result = prime_factors($n);
    print "Number: $n , Prime_Factors: => @result", "\n";
}

use Benchmark qw(cmpthese);
cmpthese( -10, {
    once =>  sub { prime_factors($_)        for @list },
    every => sub { prime_factors_sqrt($_)   for @list },
});
__END__
...
        Rate  once every
once  16.9/s    --  -94%
every  286/s 1593%    --