-- The sequence of triangle numbers is generated by adding the natural numbers
-- So the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28
-- The first ten terms would be:

-- 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...

-- Let us list the factors of the first seven triangle numbers:

--  1: 1
--  3: 1,3
--  6: 1,2,3,6
-- 10: 1,2,5,10
-- 15: 1,3,5,15
-- 21: 1,3,7,21
-- 28: 1,2,4,7,14,28
-- We can see that 28 is the first triangle number to have over five divisors

-- What is the value of the first triangle number
-- to have over five hundred divisors?

-- http://stackoverflow.com/a/32172277
triangulars = scanl (+) 1 [2 ..]

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

numDivisors :: Int -> Int
numDivisors num = (length [x | x <- [1 .. isqrt num], num `mod` x == 0]) * 2

firsTriangleWithNDivisors n = takeWhile (==n) (map numDivisors triangulars)
