# Aptitude - Odd Man Out and Series - Discussion

### Discussion :: Odd Man Out and Series - Find Wrong No. (Q.No.7)

Find out the wrong number in the series.

7.

1, 3, 10, 21, 64, 129, 356, 777

 [A]. 10 [B]. 21 [C]. 64 [D]. 129 [E]. 356

Explanation:

A x 2 + 1, B x 3 + 1, C x 2 + 1, D x 3 + 1 and so on.

So, 356 is wrong.

 Nagendramurthy said: (Jun 20, 2011) Alternate method: 1=1 3=3 10=1+0=1 21=2+1=3 64=6+4=10=1+0=1 129=1+2+9=12=1+2=3 356=3+5+6=14=1+4=5( wrong one.. it should be 1) 777=7+7+7=21=2+1=3 Alternative 1 and 3 series.. this is method is correct..

 Imran said: (Sep 21, 2011) a-1 and b=3 take first two number as a and b 1*2+1=3 3*3+1=10 10*2+1=21 21*3+1=64 64*2+1=129 129*3+1=388 but in the queston in 356 so 356 is worng 388*2+1=777 Is it clear 356 is wrong

 Sweety said: (Jan 24, 2014) 1, 3, 10, 21, 64, 129, 356, 777 3-1=2. 10-3=7. 21-10=11. 64-21=43. 129-64=65. 356-129=127. 777-356=421. Answer should be 129. Because after subtracting in all the case give prime number except in 129-64 case.

 Sarvani said: (Aug 5, 2016) 64 is a perfect square number, rest all are not.

 Kuldeep Choudhary said: (Nov 5, 2016) One more alternative method:-. Separate out even & odd place numbers as 3, 21, 129, 777 & 1, 10, 64, 356. Then find the difference between each other like 18, 108, 548 & 9, 54, 292. Hereafter you will find the division of numbers are constant (i.e. Dividend=6), only 292 differs, then back this & 356 is the answer.

 Ankush said: (May 27, 2017) Agree @Imran.

 Anu said: (Aug 2, 2017) Thanks for the explanation.

 Aditya Kavlekar said: (Oct 28, 2018) As per my logic;. Only 10 is multiple of 5 and rest are not. So odd one is 10.

 Dhara said: (May 31, 2019) I think 64 should be the answer. We are adding prime no 1 3 7 11 13 so 64 is wrong.