This is pretty good, you captured, I believe, most of the recommended optimizations.

In the beginning of your program, for better efficiency, you should have this line: 

my $max = sqrt($num);

[download]
after the while loop, so that you better benefit from the size reduction associated with the elimination of the powers of two from the original target number.

In the foreach loop, you could recalculate $max immediately after having modified $num (this will be efficient for some input data, such as the product of two or a few large primes), but, for safety, you would need to restart the foreach loop with a redo. Actually, it would be easier, clearer and safer to rewrite this loop as a while loop.

In reply to Re^9: Avoid keeping larger lists in Memory by Laurent_R
in thread Avoid keeping larger lists in Memory by pr33

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.