a(n) = 9^n-1.

Terms

a(0) =0a(1) =8a(2) =80a(3) =728a(4) =6560a(5) =59048a(6) =531440a(7) =4782968a(8) =43046720a(9) =387420488a(10) =3486784400a(11) =31381059608a(12) =282429536480