Which recurrence defines the sequence 1,2,4,8,…1, 2, 4, 8, \dots1,2,4,8,…?
an=an−1+2a_n = a_{n-1} + 2an=an−1+2
an=2an−1a_n = 2a_{n-1}an=2an−1
an=an−1+na_n = a_{n-1} + nan=an−1+n
an=an−1+1a_n = a_{n-1} + 1an=an−1+1