a(n) = 10^(2n+1) - 1 - 9*10^n.A332190a(n) = 10^(2n+1) - 1 - 9*10^n.Terms a(0) =0a(1) =909a(2) =99099a(3) =9990999a(4) =999909999a(5) =99999099999External referencesoeis: A332190