Find the number that can replace the question mark in the series given below: -1, 0, 3, 8, 15, 24, ?

The next term is 35.

The differences between terms are 1, 3, 5, 7, 9.

These are consecutive odd numbers, so the next gap is 11.

Adding, 24 + 11 = 35.

Equivalently each term is n^2 - 1, and 6^2 - 1 = 35.