let divisible_by n =
  List.filter (fun m -> m mod n <> 0)

let range a b =
  let rec range_iter a b accum =
    if b < a then
      accum
    else
      range_iter a (b - 1) (b :: accum) in
  range_iter a b []

let sieve max =
  let rec sieve_aux = function
    | [] -> []
    | x :: xs as l ->
      if x * x > max then l else x :: sieve_aux (divisible_by x xs)
   in
     sieve_aux (range 2 max)