a(n) = 9^n - 4^n.

Terms

a(0) =0a(1) =5a(2) =65a(3) =665a(4) =6305a(5) =58025a(6) =527345a(7) =4766585a(8) =42981185a(9) =387158345a(10) =3485735825a(11) =31376865305a(12) =282412759265