Find the first 5 terms of the sequence with

a1=6 and an=2a n-1 -1 for n _>2

a. 6, 12, 24, 48, 96

b. 6, 11, 21, 41, 81

c. 6, 7, 8, 9, 10

d. 1, 2, 3, 4, 5