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ProjectEular

-- Problem 23

module Main (main) where

import Array
import qualified Common as C (proper_divisors)

main :: IO ()
main = print $ problem23 28123

problem23 :: Int -> Int
problem23 max_n = sum [ n | n <- [1..max_n], null (abundant_pairs array n) ]
    where array = listArray (1,max_n) (map is_abundant [1..max_n])

abundant_pairs :: Array Int Bool -> Int -> [(Int,Int)]
abundant_pairs array n = [ (x,(n-x)) | x <- [1..(div n 2)], array ! x, array ! (n-x) ]

is_abundant :: Int -> Bool
is_abundant n = sum (C.proper_divisors n) > n

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