a(n) = 9^n+4^n-1.

Terms

a(0) =1a(1) =12a(2) =96a(3) =792a(4) =6816a(5) =60072a(6) =535536a(7) =4799352a(8) =43112256a(9) =387682632a(10) =3487832976a(11) =31385253912a(12) =282446313696