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 A125762 #39 Mar 20 2025 15:42:23 %S A125762 0,0,1,0,0,0,0,4,0,0,16,40,0,0,194,274,0,0,2384,4719,0,0,31856,62124, %T A125762 0,0,426502,817717,0,0,5724640,10838471,0,0,75178742,142349245,0,0, %U A125762 977964587,1850941916,0,0 %N A125762 Number of planar Langford sequences. %C A125762 Enumerates the Langford sequences (counted by A014552) that have the additional property that we can draw noncrossing lines to connect the two 1s, the two 2s, ..., the two ns. For example, the four solutions for n=8 are 8642752468357131, 8613175368425724, 5286235743681417, 7528623574368141. %D A125762 D. E. Knuth, TAOCP, Vol. 4, in preparation. %H A125762 John E. Miller, <a href="http://dialectrix.com/langford.html">Langford's Problem</a> %H A125762 Edward Moody, <a href="https://github.com/EdwardMGraphite/planar-langford">Java program for enumerating planar Langford sequences</a> %H A125762 Zan Pan, <a href="https://eprint.arxitics.com/articles/langford.pdf">Conjectures on the number of Langford sequences</a>, (2021). %Y A125762 Cf. A014552, A059106. %K A125762 nonn,more %O A125762 1,8 %A A125762 _Don Knuth_, Feb 03 2007 %E A125762 a(31) from _Rory Molinari_, Feb 21 2018 %E A125762 a(32)-a(34) from _Rory Molinari_, Mar 10 2018 %E A125762 a(35) from _Rory Molinari_, May 02 2018 %E A125762 a(36)-a(42) from _Edward Moody_, Apr 02 2019