a(n) = ceiling(sqrt(8*10^n)).

Terms

a(0) =9a(1) =29a(2) =90a(3) =283a(4) =895a(5) =2829a(6) =8945a(7) =28285a(8) =89443a(9) =282843a(10) =894428a(11) =2828428a(12) =8944272a(13) =28284272a(14) =89442720a(15) =282842713a(16) =894427191a(17) =2828427125a(18) =8944271910a(19) =28284271248a(20) =89442719100a(21) =282842712475a(22) =894427191000