There are many possible answer, one of which is
Un = (-40n3 + 420n2 - 1580n + 2280)/3 for n = 1, 2, 3, ...
Chat with our AI personalities
40, 80, 120, 160, 200, 240, 280, 320, 360, 400, 440, . . .
40, 80, 120, 160, 200, 240, 280, 320, 360, 400
40, 80, 120, 160, 200, 240, 280, 320, 360, 400, 440, 480, 520, 560, 600, . . .
20 Each time it divides by 2... 160/2=80; 80/2=40; 40/2=20
40, 80, 120, 160, 200, 240, 280, 320, 360, 400, 440, 480, 520, 560.