Math Help - Find a closed form

1. Find a closed form

Write a closed from function for:

F(0) = 0
F(1) = 1
F(2) = 4

F(n) = 3 + (F(n-1) - F(n-2)) + F(n-3) + 3

I can't seem to figure this one out....

2. F(n) = $n^2$

3. Oh i see it now