Answer:
n(n+1)
Step-by-step explanation:
Only the last two formulas work for n=1; only the last formula works for n=2.
For n=1
3n = 3 ≠ 2
n² -1 = 0 ≠ 2
n² +1 = 2
n(n+1) = 2
For n=2
n²+1 = 5 ≠ 6
n(n+1) = 6 . . . . . this last formula works for the given sequence
