fun prime n a 0 = a
  | prime n a i =
  if n mod 2 <> 0 andalso n mod 3 <> 0 then
    prime (n + 1) (a @ [n]) (i - 1)
  else
    prime (n + 1) a i


fun goedel n =
let
  val p = prime 5 [2, 3] 10
  val a = map (valOf o Int.fromString o str) ((explode o Int.toString) n)
in
  floor (ListPair.foldl (fn (x, y, z) => Math.pow (real x, real y) * z) 1.0 (p, a))
end

val printInt = println o Int.toString;

printInt (goedel 9);
printInt (goedel 81);
printInt (goedel 230)