Prime Number

prime_number.php

<?php

$sum = 2;

for ($i = 3; $i <= 10000; $i++) {
  $k = 1;

  for ($j = 2; $j < $i; $j++) {
    if ($i % $j == 0) {
      $k = 0;
      break;
    }
  }

  if ($k == 1) {
    echo $i . "\n";
    $sum =  $sum + $i;
  }

}

echo $sum . "\n";

?>

If you check for the number being even above the second for then you can optimize the for check by only checking for odd numbers. Since every even number is prime.

You could also optimize this by only checking odd numbers to begin with, eliminating the need to check if the number is even all together.