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 A026222 #10 Jul 04 2021 13:02:17
%S A026222 1,3,9,15,24,27,33,42,45,51,60,69,72,78,81,87,96,99,105,114,123,126,
%T A026222 132,135,141,150,153,159,168,177,180,186,195,204,207,213,216,222,231,
%U A026222 234,240,243,249,258,261,267,276,285,288,294,297
%N A026222 Numbers k such that A026136(k) = A026142(k).
%H A026222 Michael De Vlieger, <a href="/A026222/b026222.txt">Table of n, a(n) for n = 1..10000</a>
%H A026222 F. M. Dekking, <a href="https://arxiv.org/abs/2001.08915">Permutations of N generated by left-right filling algorithms</a>, arXiv:2001.08915 [math.CO], 2020.
%t A026222 Block[{nn = 10^3, a, b, s, t}, a[1] = b[1] = 1; Do[If[! IntegerQ[a[#1]], Set[a[#1], i], Set[a[#2], i]] & @@ {i - #, i + #} &@ Floor[i/2], {i, nn}]; s = TakeWhile[Array[a[#] &, nn], IntegerQ]; Do[If[! IntegerQ[b[#1]], Set[b[#1], i], Set[b[#2], i]] & @@ {i - #, i + #} &@ Floor[(i + 1)/2], {i, nn}]; t = TakeWhile[Array[b[#] &, nn], IntegerQ]; Select[Range@ Min[Last /@ {s, t}], s[[#]] == t[[#]] &]] (* _Michael De Vlieger_, Apr 21 2020 *)
%K A026222 nonn
%O A026222 1,2
%A A026222 _Clark Kimberling_