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 A217806 #11 Feb 17 2018 10:48:27 %S A217806 1,4,28,260,2844,34564,451868,6231556,89510428 %N A217806 Number of alternating permutations on 2n letters that avoid a certain pattern of length 4 (see Lewis, 2012, Appendix, for precise definition). %H A217806 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 A217806 Cf. A181197, A217799-A217830. %K A217806 nonn,more %O A217806 1,2 %A A217806 _N. J. A. Sloane_, Oct 12 2012 %E A217806 a(7)-a(9) from _Lars Blomberg_, Feb 17 2018