Find out the wrong number in the series:

Find out the wrong number in the series: 1, 3, 10, 21, 64, 129, 356, 777


Pattern mentioned is: A x 2 + 1, B x 3 + 1, C x 2 + 1, D x 3 + 1, and so on


Pattern check:



  •      T1 = 1

  • T2 = T1 × 2 + 1 = 1 × 2 + 1 = 3

  • T3 = T2 × 3 + 1 = 3 × 3 + 1 = 10

  • T4 = T3 × 2 + 1 = 10 × 2 + 1 = 21

  • T5 = T4 × 3 + 1 = 21 × 3 + 1 = 64

  • T6 = T5 × 2 + 1 = 64 × 2 + 1 = 129

  • T7 = T6 × 3 + 1 = 129 × 3 + 1 = 388 (Wrong) (but in the series it is 356)


So, T7 = 356 is incorrect - it should be 388 based on the pattern.



  1. Double-check T8:


    • If T7 were correct:
      T8 = 356 × 2 + 1 = 713 (but T8 is 777 Wrong)



If T7 is corrected to 388: T8 = 388 × 2 + 1 = 777 Correct