a(n) is the concatenation of n and 9n.

Terms

a(0) =19a(1) =218a(2) =327a(3) =436a(4) =545a(5) =654a(6) =763a(7) =872a(8) =981a(9) =1090a(10) =1199a(11) =12108a(12) =13117a(13) =14126a(14) =15135a(15) =16144a(16) =17153a(17) =18162a(18) =19171a(19) =20180a(20) =21189a(21) =22198a(22) =23207a(23) =24216a(24) =25225a(25) =26234a(26) =27243a(27) =28252a(28) =29261a(29) =30270