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 A071273 #4 Mar 14 2023 17:07:35
%S A071273 11,22,33,44,55,66,77,88,99,110,1111,2112,3113,4114,5115,6116,7117,
%T A071273 8118,9119,220,1221,2222,3223,4224,5225,6226,7227,8228,9229,330,1331,
%U A071273 2332,3333,4334,5335,6336
%N A071273 Concatenation of R(n) (A004086) and n, omitting leading 0's.
%e A071273 a(12) = 2112, a(1235) = 53211235
%t A071273 Table[10^IntegerLength[n] IntegerReverse[n]+n,{n,40}] (* _Harvey P. Dale_, Mar 14 2023 *)
%Y A071273 Cf. A071274.
%K A071273 nonn,base
%O A071273 1,1
%A A071273 _Amarnath Murthy_, Jun 07 2002