3,11, 18 , 33 , 65 , 123 , 216
8, 7, 15, 32, 58, 93
-1, 8, 17, 26, 35
9, 9, 9, 9.........., so, your sequence would continue like this:
3, 11, 18, 33, 65, 123, 216, 353, 543, 795........etc.
P.S. You could also use this formula to give any term that you want:
a(n) = 1/2 (3n^3 - 19n^2 + 52n - 30)