Let the first n terms of sequence {an} and Sn = N2, then A8=______ .

Let the first n terms of sequence {an} and Sn = N2, then A8=______ .

∵ an = sn-sn-1 (n ≥ 2), Sn = N2 ∵ A8 = s8-s7 = 64-49 = 15, so the answer is 15