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 A169774 #13 Jul 01 2017 22:59:33 %S A169774 2,0,0,4,12,20,28,120,104,304,384,1304,1680,4936,5908,18304,21412, %T A169774 63440,76920,233248,281284,833720,990104,2993016,3523740,10485472, %U A169774 12432392,37485424,44184884,131430320,154630088,465106072,544994604,1622783328,1904647128 %N A169774 Number of open knight's tour diagrams of a 3 X n chessboard that are symmetric under 180-degree rotation and have "type F": the endpoints occur in different columns and agree in color with the cells in the nearest corner. %D A169774 D. E. Knuth, Long and skinny knight's tours, in Selected Papers on Fun and Games, to appear, 2010. %H A169774 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 A169774 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 A169774 D. E. Knuth <a href="/A169770/a169770.txt">Generating functions for A169770-A169777 and A169696.</a> %Y A169774 Cf. A070030, A169696, A169764-A169777. %K A169774 nonn %O A169774 4,1 %A A169774 _N. J. A. Sloane_, May 10 2010, based on a communication from _Don Knuth_, Apr 28 2010 %E A169774 a(31)-a(38) from _Andrew Howroyd_, Jul 01 2017