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

Terms

a(0) =1a(1) =8a(2) =77a(3) =720a(4) =6545a(5) =59024a(6) =531405a(7) =4782920a(8) =43046657a(9) =387420408a(10) =3486784301a(11) =31381059488a(12) =282429536337