coins = [2, 3, 7]

change :: Integer -> [[Integer]]
change n = foldl (\acc x -> acc ++ (nub $ permutations x)) [] result
  where result = change' coins n

change' :: [Integer] -> Integer -> [[Integer]]
change' _  0 = [[]]
change' [] _ = []
change' xxs@(x:xs) n
  | n >= x    = map (x:) (change' xxs (n - x)) ++ change' xs n
  | otherwise = change' xs n