forwardDifference xs = zipWith (-) (tail xs) xs

nthForwardDifference xs n = iterate forwardDifference xs !! n

> take 10 (iterate forwardDifference [90, 47, 58, 29, 22, 32, 55, 5, 55, 73])
[[90,47,58,29,22,32,55,5,55,73],
 [-43,11,-29,-7,10,23,-50,50,18],
 [54,-40,22,17,13,-73,100,-32],
 [-94,62,-5,-4,-86,173,-132],
 [156,-67,1,-82,259,-305],
 [-223,68,-83,341,-564],
 [291,-151,424,-905],
 [-442,575,-1329],
 [1017,-1904],
 [-2921]]