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 A026215 #13 Aug 30 2021 05:34:57
%S A026215 2,1,6,8,3,4,14,5,18,20,7,24,26,9,10,32,11,12,38,13,42,44,15,16,50,17,
%T A026215 54,56,19,60,62,21,22,68,23,72,74,25,78,80,27,28,86,29,30,92,31,96,98,
%U A026215 33,34,104,35,36,110,37,114,116,39,40,122,41
%N A026215 a(n) is the position of n in A026214.
%H A026215 Michael De Vlieger, <a href="/A026215/b026215.txt">Table of n, a(n) for n = 1..10922</a>
%H A026215 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 A026215 With[{s = Array[If[Mod[#/3^IntegerExponent[#, 3], 3] == 1, Ceiling[#/3], #] &[(6 # + 1)/4 - (-1)^#/4] &, Floor[2 #/3]] &[189]}, Array[FirstPosition[s, #][[1]] &, LengthWhile[Differences@ Union[s], # == 1 &]]] (* _Michael De Vlieger_, Aug 29 2021 *)
%Y A026215 Cf. A026214.
%K A026215 nonn
%O A026215 1,1
%A A026215 _Clark Kimberling_