Complete the series: 1, 3, 7, 15, 31, 63, ……?

A) 123

B) 125

C) 127

D) 129

Starting with the first number ‘1’, we move ahead in the way given below:

1 x 2 + 1 = 3

3 x 2 + 1 = 7

7 x 2 + 1 = 15

15 x 2 + 1 = 31

31 x 2 + 1 = 63

63 x 2 + 1 = 127

Therefore 127 is the next number in the series.