This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A009474 #19 Sep 08 2022 08:44:37
%S A009474 19,218,327,436,545,654,763,872,981,1090,1199,12108,13117,14126,15135,
%T A009474 16144,17153,18162,19171,20180,21189,22198,23207,24216,25225,26234,
%U A009474 27243,28252,29261,30270,31279,32288,33297,34306,35315,36324,37333,38342,39351
%N A009474 a(n) is the concatenation of n and 9n.
%H A009474 Vincenzo Librandi, <a href="/A009474/b009474.txt">Table of n, a(n) for n = 1..1000</a>
%t A009474 nxt[n_]:=Module[{idn=IntegerDigits[n], idn9=IntegerDigits[9n]}, FromDigits[Join[idn, idn9]]]; Array[nxt, 100] (* _Vincenzo Librandi_, Feb 04 2014 *)
%o A009474 (Magma) [Seqint(Intseq(9*n) cat Intseq(n)): n in [1..50]]; // _Vincenzo Librandi_, Feb 04 2014
%Y A009474 Cf. concatenation of n and k*n: A020338 (k=1), A019550 (k=2), A019551 (k=3), A019552 (k=4), A019553 (k=5), A009440 (k=6), A009441 (k=7), A009470 (k=8), this sequence (k=9).
%K A009474 nonn,base,less,easy
%O A009474 1,1
%A A009474 _David W. Wilson_