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

Terms

a(0) =0a(1) =90a(2) =990a(3) =9990a(4) =99990a(5) =999990a(6) =9999990a(7) =99999990a(8) =999999990a(9) =9999999990a(10) =99999999990a(11) =999999999990