If the sum of the first nnn terms of a sequence is Sn=2n+1−2S_n = 2^{n+1} - 2Sn=2n+1−2, what is the kkk-th term aka_kak?
ak=2ka_k = 2^kak=2k
ak=2k+1a_k = 2^{k+1}ak=2k+1
ak=2k−1a_k = 2^{k-1}ak=2k−1
ak=2k+2a_k = 2^{k+2}ak=2k+2