let f = function
    n when n mod 2 = 0 -> n / 2
  | n -> (3 * n + 1) / 2
                       
let make_char = function
    n when n mod 2 = 0 -> " "
  | n -> "#"

let call_nth n f init =
  let rec inner rv k = function
      m when n <= m -> List.rev rv
    | m -> let next = f k in inner ([next] @ rv) next (m + 1)
  in
  inner [init] init 0

let make_line n =
  String.concat "" (List.map make_char (call_nth 63 f n))

let () =
  for n = 256 downto -256 do
    Printf.printf "%s|\n" (make_line n)
  done