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 A026139 #13 Aug 28 2021 02:50:27
%S A026139 1,3,7,9,15,19,21,25,27,33,39,43,45,51,55,57,61,63,69,73,75,79,81,87,
%T A026139 93,97,99,105,111,115,117,123,127,129,133,135,141,147,151,153,159,163,
%U A026139 165,169,171,177,181,183,187,189,195,201,205,207,213
%N A026139 a(n) = s(k), where k is the n-th number such that s(j) < s(k) for all j < k, where s = A026136. Also a(n) = 2*t(n) - 1, where t = A026138.
%C A026139 Records in A026136. - _Michael De Vlieger_, Aug 27 2021
%H A026139 Michael De Vlieger, <a href="/A026139/b026139.txt">Table of n, a(n) for n = 1..10000</a>
%H A026139 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 A026139 Block[{a, r, s, nn = 108}, a[1] = 1; Do[If[! IntegerQ[a[#1]], Set[a[#1], i], Set[a[#2], i]] & @@ {i - #, i + #} &@ Floor[i/2], {i, 2 nn}]; s = TakeWhile[Array[a[#] &, nn], IntegerQ]; Union@ FoldList[Max, s]] (* _Michael De Vlieger_, Aug 27 2021 *)
%Y A026139 Cf. A026138.
%K A026139 nonn
%O A026139 1,2
%A A026139 _Clark Kimberling_
%E A026139 Edited by _N. J. A. Sloane_, Jan 31 2020