a(n) = Sum_{k=1..9} floor(10^n / k).

Terms

a(0) =1a(1) =26a(2) =281a(3) =2827a(4) =28288a(5) =282895a(6) =2828967a(7) =28289681a(8) =282896824a(9) =2828968252a(10) =28289682538a(11) =282896825395