-- Starting in the top left corner of a 2×2 grid, and only being able to move to the right and down, there are exactly 6 routes to the bottom right corner -- How many such routes are there through a 20×20 grid? factorial :: (Integral a) => a -> a factorial 0 = 1 factorial n = n * factorial (n - 1) main = do let result = factorial 40 `div` factorial 20 ^ 2 putStrLn $ "Project Euler, Problem 15\n" ++ "Answer: " ++ show result