Just for info, I did the same course. Didn't googled for a solution. I've come with that solution. Now I'm googling it just to see how other perl user are solving that easy problem :-) and what I see is quite interesting (especially this things with regex!!) It might not be the speediest, but still it might be of some interest to some people!

perl -le '$_=2;while($ARGV[0]-1){if(!($ARGV[0]%$_)){print$_ ;$ARGV[0]/
+=$_;}else{$_++}}' $1
[download]

or in a non-one-liner form:

$_=2;
while ($ARGV[0]-1) {
  if (!($ARGV[0]%$_)) {
    print $_ ;
    $ARGV[0]/=$_;
  } else {
    $_++
  }
}
[download]

Sincerely yours, Alessandro