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

Terms

a(0) =1a(1) =27a(2) =405a(3) =5103a(4) =59049a(5) =649539a(6) =6908733a(7) =71744535a(8) =731794257a(9) =7360989291a(10) =73222472421a(11) =721764371007