Two sequences are defined by coupled recurrences: an=2bn−1a_n = 2b_{n-1}an=2bn−1 and bn=an−1+bn−1b_n = a_{n-1} + b_{n-1}bn=an−1+bn−1 with a0=1,b0=1a_0 = 1, b_0 = 1a0=1,b0=1. What is a3a_3a3?
444
666
888
101010