a(n) = 9^n - 5^n.

Terms

a(0) =0a(1) =4a(2) =56a(3) =604a(4) =5936a(5) =55924a(6) =515816a(7) =4704844a(8) =42656096a(9) =385467364a(10) =3477018776a(11) =31332231484a(12) =282185395856