a(n) = (10^n - 1)*(80/81) + n/9.

Terms

a(0) =9a(1) =98a(2) =987a(3) =9876a(4) =98765a(5) =987654a(6) =9876543a(7) =98765432a(8) =987654321a(9) =9876543210a(10) =98765432099a(11) =987654320988