# Aptitude - Odd Man Out and Series - Discussion

Discussion Forum : Odd Man Out and Series - Find Wrong No. (Q.No. 10)
Directions to Solve
Find out the wrong number in the series.

10.
3, 7, 15, 39, 63, 127, 255, 511
7
15
39
63
127
Explanation:

Go on multiplying 2 and adding 1 to get the next number.

So, 39 is wrong.

Discussion:
8 comments Page 1 of 1.

Nani said:   6 years ago
All are divisible by 3. But 7 can't be divisible. So, why can't that be the answer?
(1)

R@m said:   7 years ago
The another logic is 2^2 - 1, 2^3 - 1, 2^4 - 1, .....

Poooja said:   7 years ago

Mehtab said:   8 years ago
3*2 + 1 = 7
7*2 + 1 = 15
15*2 + 1 = 31
31*2 + 1 = 63
63*2 + 1 = 127
127*2 + 1 = 255
255*2 + 1 = 511

31 is given instead of 31.

Siva said:   8 years ago

Grace said:   10 years ago
3+4 = 7.
7+8 = 15.
15+16 = 31.
31+32 = 63.
63+64 = 127.
127+128 = 255.
255+256 = 511.
.
.

It can also be solved like such---
2^2-1,2^3-1,2^4-1,2^5-1 and so on....

Ashik Mohammed Nazar said:   1 decade ago
3,7,15,39,63,127,255,511
If u closely look at this pattern,and the differences between the consecutive numbers,
It is 4 8 24 24 64 128 256
By changing 39 to 31, the differences become
4 8 16 32 64 128 256 which is
2^2 2^3 2^3 2^4 and so on ...