Question

QIF,S2E,U6D,W21C, ?
complete the series

Answer 1

Answer: . Y88B

The first letter of each term is moved two steps forward and

the last letter is moved one steps backward to obtain the corresponding letters of the next term.

The number series runs as follows :

1 x 1 + 1 = 2,

2 x 2 + 2 = 6,

6 x 3 + 3 = 21,

21 x 4 + 4 = 88.