Prime Number Generator

$a = microtime(true);$d = array(2,3,5,7);for ($b = 11; $b < 1000; $b += 2) {  if (($b % 3) && ($b % 5) && ($b % 7)) {    if ($b > 49) {      $e = sqrt($b);      for ($c = 4; $f = $d[$c], $f <= $e; $c++)        if (!($b % $f)) continue 2;    }    $d[] = $b;  }}printf("%01.5f",microtime(true)-$a);print_r($d);