For a sequence an=an−1+an−2a_n = a_{n-1} + a_{n-2}an=an−1+an−2 with a0=0,a1=1a_0 = 0, a_1 = 1a0=0,a1=1, what is ∑k=0nak\sum_{k=0}^n a_k∑k=0nak?
an+2−1a_{n+2} - 1an+2−1
an+1a_{n+1}an+1
an+an−1a_n + a_{n-1}an+an−1
an+2+1a_{n+2} + 1an+2+1