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 A217803 #10 Oct 08 2018 09:30:38 %S A217803 1,2,12,108,1202,15234,210696,3102296,47875884 %N A217803 Number of alternating permutations on 2n+1 letters that avoid a certain pattern of length 4 (see Lewis, 2012, Appendix, for precise definition). %H A217803 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 A217803 Cf. A181197, A217799-A217830. %K A217803 nonn,more %O A217803 0,2 %A A217803 _N. J. A. Sloane_, Oct 12 2012 %E A217803 a(6)-a(8) from _Lars Blomberg_, Jan 23 2018