exception Break;;

let sqrt_int x = int_of_float(sqrt(float_of_int x));;

let isPrime x =
  try
    for i=2 to (sqrt_int x) do
      if (x mod i) = 0 then
    raise Break;
    done;
    true;
  with
      Break -> false
;;

let rec primes x =
  let rec loop x i =
    if i = x then
      [x]
    else
      if x mod i = 0 then
    if (isPrime i) then
      i::(primes (x/i))
    else
      (primes i)@(primes (x/i))
      else
    loop x (i+1)
  in
  loop x 2
;;

List.iter (fun x-> print_int x; print_string " ") (primes 18);;


(*
output:
eni@rocket:~/Documents/code/ocaml$ ocaml primes.ml
2 3 3
*)