a(n) = 4^n + 6^n + 9^n.

Terms

a(0) =3a(1) =19a(2) =133a(3) =1009a(4) =8113a(5) =67849a(6) =582193a(7) =5079289a(8) =44791873a(9) =397760329a(10) =3548299153a(11) =31748050969a(12) =284623096033