my $f1;
my $c = <>; # get number

# Get factor and the new number to test
while ($c > 1) {
   ($f1,$c) = get_a_factor($c);
   print ", $f1";
}

print "\n";

sub get_a_factor {
   my $num = shift;
   ... compute factor ...
   return ($factor, $num/$factor);
}