Question

insert the missing number. 4, 9, 17 , 35 , ? , 139

Answer 1

Your answer is 69, buddy.
4*2+1=9
9*2-1=17
17*2+1=35
35*2-1=69
69 is the answer.
Pattern continued...
... 69*2+1=139 (Verified)

Answer 2

4× 2 +1=9

9× 2 -1= 17

17× 2 +1= 35

35× 2 -1= 69

69× 2 +1= 139

So 69 is the answer