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

Terms

a(0) =1a(1) =19a(2) =199a(3) =1999a(4) =19999a(5) =199999a(6) =1999999a(7) =19999999a(8) =199999999a(9) =1999999999a(10) =19999999999a(11) =199999999999