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 A233138 #4 Dec 07 2013 12:56:54
%S A233138 1,2,1,2,2,2,1,2,2,2,1,2,1,2,1,2,2,2,2,1,2,2,2,2,1,2,2,1,2,1,2,2,2,2,
%T A233138 1,2,1,2,2,1,2,2,1,2,1,2,1,2,1,2,1,2,2,2,2,2,1,2,2,2,2,2,1,2,2,2,1,2,
%U A233138 1,2,2,2,2,2,1,2,2,1,2,2,1,2,2,2,1,2
%N A233138 Concatenated reversed shortest (x+1,2x)-codes for the positive integers.
%C A233138 Concatenate the representations of the positive integers in A233137, and then separate the digits by commas.
%H A233138 Clark Kimberling, <a href="/A233138/b233138.txt">Table of n, a(n) for n = 1..10000</a>
%e A233138 A233137 = (1,2,12,22,122,212,...), so that A233138 = (1,2,1,2,2,2,1,2,2,2,1,2,...)
%t A233138 b[x_] := b[x] = If[OddQ[x], x - 1, x/2]; u[n_] := 2 - Mod[Drop[FixedPointList[b, n], -3], 2]; u[1] = {1}; t = Table[u[n], {n, 1, 30}]; Table[FromDigits[u[n]], {n, 1, 50}] (* A233137 *)
%t A233138 Flatten[t] (* A233138 *)
%t A233138 Table[FromDigits[Reverse[u[n]]], {n, 1, 30}] (* A233135 *)
%t A233138 Flatten[Table[Reverse[u[n]], {n, 1, 30}]] (* A233136 *)
%Y A233138 Cf. A040039, A135529, A232559, A000045, A233135, A233137, A233138.
%K A233138 nonn,easy
%O A233138 1,2
%A A233138 _Clark Kimberling_, Dec 05 2013