munchausen

{-# LANGUAGE NumericUnderscores #-}

import Data.Array.Unboxed

cache :: UArray Int Int
cache = listArray (0, 9) $ 0:[i^i | i <- [1..9]]

recourse :: (Int -> Int) -> (Int, Int) -> Int
recourse f (q, r) = cache ! r + f q

calc :: Int -> Int
calc n
  | n > 0 = recourse calc $ n `quotRem` 10
  | otherwise = 0

isMunchausen :: Int -> Bool
isMunchausen n = (calc n) == n

main = do
  mapM_ print $ filter (\i -> isMunchausen i) [0 .. 440_000_000]
  return 0