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

Terms

a(0) =2a(1) =13a(2) =97a(3) =793a(4) =6817a(5) =60073a(6) =535537a(7) =4799353a(8) =43112257a(9) =387682633a(10) =3487832977a(11) =31385253913a(12) =282446313697