a(n) = 9^n - 8.

Terms

a(0) =1a(1) =73a(2) =721a(3) =6553a(4) =59041a(5) =531433a(6) =4782961a(7) =43046713a(8) =387420481a(9) =3486784393a(10) =31381059601a(11) =282429536473