function array_range($from, $to, $step=1){
  $array = array();
  for ($x=$from; $x <= $to; $x += $step){
    $array[] = $x;
  }
  return $array;
}
print_r(array_range(0, 20, 5));
/*
returns:
Array
(
  [0] => 0
  [1] => 5
  [2] => 10
  [3] => 15
  [4] => 20
)
*/