I am almost sure this does what you want. I am also convinced it is rather inefficient. 
my @res = (2, 2, 2, 5, 5, 5);
my $goal = 1000;

print closest($goal, \@res), "\n";

sub closest{
    my $exact = shift;
    my $array = shift;

    my $best = 0;

    for my $n ( get_numbers($array) ){
        $best = $n if abs( $exact - $n**2) < abs( $exact - $best**2);
    }
    $best;
}

sub get_numbers{
    my $array = shift;

    my $length = @$array;

    if ($length == 1){
        return ( $array->[0] );
    }
    else{
        my @ret_arr;
        my $n = shift @$array;
        push @ret_arr, $n;
        my @tmp = get_numbers($array);
        push @ret_arr, @tmp;
        push @ret_arr, $n*$_ for @tmp;
        prune(@ret_arr);
    }
}

sub prune{
    my %h;

    undef $h{$_} for @_;
    keys %h;
}

[download]
Uppdate: Cleaned up it a little,removing some(most) of the inefficiense.

In reply to Re: OT: Finding Factor Closest To Square Root by lidden
in thread OT: Finding Factor Closest To Square Root by QM

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.