a(n) = 2*(10^n - 1).

Terms

a(0) =0a(1) =18a(2) =198a(3) =1998a(4) =19998a(5) =199998a(6) =1999998a(7) =19999998a(8) =199999998a(9) =1999999998a(10) =19999999998a(11) =199999999998