import Data.Char (digitToInt) digitFactorial :: Integer -> Integer digitFactorial n = case n of 0 -> 1 1 -> 1 2 -> 2 3 -> 6 4 -> 24 5 -> 120 6 -> 720 7 -> 5040 8 -> 40320 9 -> 362880 loops :: Integer -> Maybe Integer loops n | n `elem` [169, 363601, 1454] = Just 3 | n `elem` [871, 872, 45361, 45362] = Just 2 | n `elem` [1, 2, 145, 40585] = Just 1 | otherwise = Nothing sumOfFactorialOfDigits :: Integer -> Integer sumOfFactorialOfDigits n = sum $ map (digitFactorial . fromIntegral . digitToInt) $ show n getChainLength :: Integer -> Integer getChainLength n = getChainLengthRec n 1 getChainLengthRec :: Integer -> Integer -> Integer getChainLengthRec n length = let next = sumOfFactorialOfDigits n in case loops next of Just x -> length + x Nothing -> getChainLengthRec next (length + 1) numOfLoops :: Integer -> Integer -> Integer numOfLoops bound length = foldr (\n num -> num + if getChainLength n == length then 1 else 0) 0 [3..bound] main = print $ numOfLoops 1000000 60