Find the first six terms of the sequence.
a1 = 1, an = 4 • an-1

A) 0, 4, 4, 8, 12, 16
B) 4, 16, 64, 256, 1024, 4096
C) 1, 4, 8, 12, 16, 20
D) 1, 4, 16, 64, 256, 1024