a(n) = 9^n + 2^n - 1.

Terms

a(0) =1a(1) =10a(2) =84a(3) =736a(4) =6576a(5) =59080a(6) =531504a(7) =4783096a(8) =43046976a(9) =387421000a(10) =3486785424a(11) =31381061656a(12) =282429540576