6 7 9 13 26 37 69
May be this question is to identify the wrong number in the series...
6 - 7: 1 <-- 2^0
7 - 9: 2 <-- 2^1
9 - 13: 4 <-- 2^2
13 - 21: 8 <-- 2^3 to get a difference of 2^3; the 5th term should be 21, instead of 26.
21 - 37: 16 <-- 2^4
37 - 69: 32 <-- 2^5
So, the wrong number is: 26
Option: 2