a(n) = Sum_{d|n} phi(d)*9^(n/d).

Terms

a(0) =0a(1) =9a(2) =90a(3) =747a(4) =6660a(5) =59085a(6) =532350a(7) =4783023a(8) =43053480a(9) =387422001a(10) =3486843810a(11) =31381059699a(12) =282430082700