a(n) = 0^n + 10^n - 1.

Terms

a(0) =1a(1) =9a(2) =99a(3) =999a(4) =9999a(5) =99999a(6) =999999a(7) =9999999a(8) =99999999a(9) =999999999a(10) =9999999999a(11) =99999999999a(12) =999999999999