Question

insert the missing number . 16,33,65,131,261, __​

Answer 1

16 ,33 , 65 , 131 , 261 , __

♥ Each number is twice the preceding one with 1 added or subtracted alternatively .

So, the next number is (2 x 261 + 1) = 523 .

Answer 2

$answer -$

523 is your answer.