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 A169773 #12 Jul 01 2017 22:59:21 %S A169773 0,0,0,0,0,4,0,0,0,16,0,0,0,264,0,0,0,2144,0,0,0,22408,0,0,0,211808,0, %T A169773 0,0,2087344,0,0,0,20207664,0,0,0,197082624,0,0,0,1916054112,0,0,0, %U A169773 18652927040,0,0,0,181485750208,0,0,0,1766199186560,0,0,0 %N A169773 Number of open knight's tour diagrams of a 3 X n chessboard that are symmetric under 180-degree rotation and have "type X": both endpoints occur in the same column. %D A169773 D. E. Knuth, Long and skinny knight's tours, in Selected Papers on Fun and Games, to appear, 2010. %H A169773 George Jelliss, <a href="http://www.mayhematics.com/t/oa.htm">Open knight's tours of three-rank boards</a>, Knight's Tour Notes, note 3a (21 October 2000). %H A169773 George Jelliss, <a href="http://www.mayhematics.com/t/ob.htm">Closed knight's tours of three-rank boards</a>, Knight's Tour Notes, note 3b (21 October 2000). %H A169773 D. E. Knuth <a href="/A169770/a169770.txt">Generating functions for A169770-A169777 and A169696.</a> %F A169773 A169773(n)=0 unless n mod 4 = 1. %Y A169773 Cf. A070030, A169696, A169764-A169777. %K A169773 nonn %O A169773 4,6 %A A169773 _N. J. A. Sloane_, May 10 2010, based on a communication from _Don Knuth_, Apr 28 2010 %E A169773 a(31)-a(60) from _Andrew Howroyd_, Jul 01 2017