1, 2, 7, ?, 111, 564

Find out the missing number in the following number series.

1) 1, 2, 7, ?, 111, 564

A.28

B.26

C.14

D.21

E.18

Sol:

1 * 1 + 1 = 2

26 * 4 + 7 = 111

111 * 5 + 9 = 564

2 * 2 + 3 = 7

7 * 3 + 5 = 26