http://math.stackexchange.com/a/1142082/2582

gistfile1.hs

module Main
    where


perfectSquares :: [Int]
perfectSquares = map (^2) [1..100]

divisors :: Int -> [(Int, Int)]
divisors n = [ (i, div n i) | i <- [1..floor $ sqrt $ fromIntegral n]
             , mod n i == 0]

transformPairs :: [(Int, Int)] -> [(Int, Int)]
transformPairs = map (\(a, b) -> ((a + b) `div` 2, (b - a) `div` 2))

isqrt :: Int -> Int
isqrt = floor . sqrt . fromIntegral

solve :: Int -> [(Int, Int)]
solve n = [ (x, isqrt y) | (x, y) <- transformPairs $ divisors n
          , y `elem` perfectSquares]

main :: IO ()
main = print $ solve 336