a(n) = 1^n + 2^n + 9^n.

Terms

a(0) =3a(1) =12a(2) =86a(3) =738a(4) =6578a(5) =59082a(6) =531506a(7) =4783098a(8) =43046978a(9) =387421002a(10) =3486785426a(11) =31381061658a(12) =282429540578