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 A217807 #14 Feb 19 2018 18:16:10 %S A217807 1,4,29,292,3620,51866,827415,14350467,266218320 %N A217807 Number of alternating permutations on 2n letters that avoid a certain pattern of length 4 (see Lewis, 2012, Appendix, for precise definition). %H A217807 Andrew R. Conway, Anthony J. Guttmann, Paul Zinn-Justin, <a href="https://arxiv.org/abs/1709.01248">1324-avoiding permutations revisited</a> arXiv:1709.01248 [math.CO], 2017. %H A217807 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 A217807 Cf. A181197, A217799-A217830. %K A217807 nonn,more %O A217807 1,2 %A A217807 _N. J. A. Sloane_, Oct 12 2012 %E A217807 a(7)-a(9) from _Lars Blomberg_, Feb 17 2018