triangleNumbers :: [Int]
triangleNumbers = snd <$> iterate (\(i,f) -> (i+1, i+f+1)) (1,1)
triangleNumbers :: [Int]
triangleNumbers = snd <$> iterate (\(i,f) -> (i+1, i+f+1)) (1,1)
triangleNumbers = snd <$> iterate (\(i,f) -> (i+1, i+f+1)) (1,1)