-- Starting with the number 1 and moving to the right in a clockwise direction
-- a 5 by 5 spiral is formed as follows:
--
--   21 22 23 24 25
--   20  7  8  9 10
--   19  6  1  2 11
--   18  5  4  3 12
--   17 16 15 14 13
--
-- It can be verified that the sum of the numbers on the diagonals is 101.
--
-- What is the sum of the numbers on the diagonals in a 1001 by 1001 spiral
-- formed in the same way?

ne = 1 : zipWith (+) nw [2,4..]
se =     zipWith (+) ne [2,4..]
sw =     zipWith (+) se [2,4..]
nw =     zipWith (+) sw [2,4..]

-- Sum of diagonals of an m by m spiral; m = 2*n + 1.
diagSum n = sum (take (n+1) ne ++ take n se ++ take n sw ++ take n nw)

main = print $ (diagSum 2, diagSum 500)