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 A175881 #25 May 05 2025 15:06:50 %S A175881 0,0,0,0,8,9862,1067638,55488142,3374967940,239187240144, %T A175881 15360134570696,964730606632516,61989683445413228,4005716717182224826, %U A175881 255967892553030600920,16378998506224697063588,1050504687249683771795632,67351449674771471216148786,4314151246752166099728445868 %N A175881 Number of closed Knight's tours on a 6 X n board. %C A175881 Could you please say how you calculated these numbers? - _N. J. A. Sloane_, Dec 05 2010? %C A175881 I kept track of pairs of loose ends within the two rightmost columns of a 6 X n board, assuming that everything to the left of these two columns is fully connected and that there are no cycles (or one if this is a final state). Next I added a new column and connected it to the rightmost two columns in all ways such that there are no cycles formed(or one if this results in a final state) and the leftmost column in the current state is fully connected and can be dropped. From this followed a transition matrix. I can provide a reference to my writeup once it is completed and has been accepted by my supervisor. - _Johan de Ruiter_, Dec 05 2010 %H A175881 Johan de Ruiter, <a href="/A175881/b175881.txt">Table of n, a(n) for n = 1..40</a> %H A175881 J. de Ruiter, <a href="http://www.math.leidenuniv.nl/~jruiter/CountingDominoCoveringsAndChessboardCycles.pdf">Counting Domino Coverings and Chessboard Cycles</a>, 2010. %F A175881 a(n) = A383662(3n). - _Don Knuth_, May 05 2025 %e A175881 The smallest 6 X n board admitting a closed Knight's tour is the 6 X 5, on which there are 8 such tours. %Y A175881 A070030 deals with 3 X 2n boards, A175855 with 5 X 2n boards. %Y A175881 Cf. A383662. %K A175881 nonn %O A175881 1,5 %A A175881 _Johan de Ruiter_, Dec 05 2010