10^n-10^(n-2).

Terms

a(0) =1a(1) =10a(2) =99a(3) =990a(4) =9900a(5) =99000a(6) =990000a(7) =9900000a(8) =99000000a(9) =990000000a(10) =9900000000a(11) =99000000000a(12) =990000000000