Glad I waited until you posted first! But here is my contribution, non-destructive of the array. Replace the while{} with the following:

OUTER: for (my $r = 0; $r < @primeNumbers; $r += $NumPerRow) {
  for (my $c = r; $c - $r < $NumPerRow; $c++) {
    printf $format, $primeNumbers[$c];
    last OUTER if ($c == $#primeNumbers);
  }
  print "\n";
}
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