Question

What is the next number?
2, 7, 26, 101, 400, ?

Answer 1

7/2=3.5
26/7=3.7
101/26=3.9
400/101=4
400 x 4 or 4.1 = 1600 or 1640

Answer 2

It is 1595. Put it on excel so you can better have an overview how it is done. You need 5 columns, column A-E. On column A, put 1 to 5 in rows 1 to 5. On column C, put the answers: 2, 7, 26, 101 and 400. On column D, put number 3 in all 5 rows. Back on column B, insert =sum(C1-A1) on row 1 and copy till row 5. On column E, insert =sum(B1+C1*D1) on row 1 and copy till row 5 and you will get 1595 at the end.