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 A217820 #8 Oct 08 2018 09:30:38 %S A217820 1,5,61,1194,30802,953088,33563745,1302192441 %N A217820 Number of alternating permutations on 2n letters that avoid a certain pattern of length 5 (see Lewis, 2012, Appendix, for precise definition). %H A217820 J. B. Lewis, <a href="https://dspace.mit.edu/handle/1721.1/73444">Pattern Avoidance for Alternating Permutations and Reading Words of Tableaux</a>, Ph. D. Dissertation, Department of Mathematics, MIT, 2012. %Y A217820 Cf. A181197, A217799-A217830. %K A217820 nonn,more %O A217820 1,2 %A A217820 _N. J. A. Sloane_, Oct 13 2012 %E A217820 a(7)-a(8) from _Lars Blomberg_, Feb 28 2018