-- 145 is a curious number, as 1! + 4! + 5! = 1 + 24 + 120 = 145. -- -- Find the sum of all numbers which are equal to the sum of the factorial of their digits. -- -- Note: as 1! = 1 and 2! = 2 are not sums they are not included. import Data.Char factorial :: (Integral a) => a -> a factorial 0 = 1 factorial n = n * factorial (n - 1) factDigits :: [Int] factDigits = map factorial [0..9] equalsDigitFactorial :: Int -> Bool equalsDigitFactorial n = let fact_digit_sum = sum $ [ factDigits !! x | x <- map digitToInt (show n) ] in fact_digit_sum == n main = do let result = sum $ filter equalsDigitFactorial [10..9999999] putStrLn $ "Project Euler, Problem 34\n" ++ "Answer: " ++ show result