What is the nth term of the sequence below?

2, 6, 12, 20, . . .

A. [tex]n {}^{2} \: + \: 1[/tex]

B. [tex]3n[/tex]

C. [tex]n(n \: + \: 1)[/tex]

D. [tex] {n}^{2} \: - \: 1[/tex]