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 A217810 #14 Jun 06 2020 03:35:17 %S A217810 1,5,42,454,5680,78129 %N A217810 Number of alternating permutations on 2n letters that avoid a certain pattern of length 4 (see Lewis, 2012, Appendix, for precise definition). %H A217810 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. See Table A.2. %Y A217810 Cf. A181197, A217799-A217830. %K A217810 nonn,more %O A217810 1,2 %A A217810 _N. J. A. Sloane_, Oct 13 2012 %E A217810 Data corrected by _Andrew Howroyd_ after observation by _Gionata Neri_, May 02 2020