The last obfuscation w.r.t. fft got me inspired, so I spent some of my CPU time to do this:

print join (' ', map {
   srand ($_->[0]);
   my $l;
   for (1..$_->[1]) {
      $l = ''; $l .= chr (int (rand (58))+65) for 1..6;
   }  
   substr ($l, 0, $_->[0] < 1024 ? 4 : 6)
} [346, 5305], [59235, 9374], [512, 2698], [104315, 5127]), "\n";
[download]

I hope it works everywhere, as I'm not sure whether srand&rand have the same algo everywhere.