Mathematics for IGCSE & O level - Sequences (Section 4 - No. 24)

What is the nth term formula of this quadratic sequence: 2, 5, 10, 17, 26, ...?

n^2 + 1

2n^2 -1

3n + 2

n + 2

The differences between terms are 3, 5, 7, 9 which increases by 2. Thus, the formula is n^2 + 1.