cat4 :: [Integer]
cat4 = map c [0 ..]
  where c n = sum (map (\k -> binom n k ^ 2) [0 .. n]) `div` (n + 1)
cat4 :: [Integer]
cat4 = map c [0 ..]
  where c n = sum (map (\k -> binom n k ^ 2) [0 .. n]) `div` (n + 1)
cat4 = map c [0 ..]
  where c n = sum (map (\k -> binom n k ^ 2) [0 .. n]) `div` (n + 1)