my $itemLength = length($iterations);
#account for comma and 1 space extra, but at least 1 number per row!
my $NumPerRow = int(80/($itemLength+2)) || 1; 
my $format = "%0${itemLength}d, ";
while (@primeNumbers)
{
  printf($format, shift @primeNumbers) for (1..$NumPerRow);
  print "\n";
}