Problem 21
http://projecteuler.net/index.php?section=problems&id=21
--Haskell, 20090101 import List (nub) divisors :: Int -> Int divisors n = sum $ 1 : concat [nub [x, n`div`x] | x<-takeWhile ((<=n).(^2)) [2..], n`mod`x==0] main = print $ sum [x | x<-[1..9999], let y = divisors x, y /= x, x == divisors y]