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 A278993 #19 Nov 03 2021 06:03:43 %S A278993 0,1,1,4,21,176,1893,25030,382272,6604535,127222636,2702798537, %T A278993 62778105236,1582725739329,43046433007765,1256332883208474, %U A278993 39165907107963273,1298945495674093932,45666536827274985585,1696460750775267473762 %N A278993 Number of simple chord diagrams with n chords, up to rotation. %H A278993 E. Krasko and A. Omelchenko, <a href="http://arxiv.org/abs/1601.05073">Enumeration of Chord Diagrams without Loops and Parallel Chords</a>, arXiv preprint arXiv:1601.05073 [math.CO], 2016. %H A278993 E. Krasko and A. Omelchenko, <a href="https://doi.org/10.37236/6037">Enumeration of Chord Diagrams without Loops and Parallel Chords</a>, The Electronic Journal of Combinatorics, 24(3) (2017), #P3.43. %Y A278993 Cf. A003436, A003437, A007474, A278990, A278991, A278992, A278994. %K A278993 nonn %O A278993 1,4 %A A278993 _N. J. A. Sloane_, Dec 07 2016