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%I #13 Jul 01 2017 23:00:09
%S 2,0,0,2,10,12,22,60,76,160,292,652,1148,2600,3870,9152,13710,32792,
%T 48112,116624,171732,428064,589842,1496508,2069766,5348640,7164172,
%U 18742712,25160796,66758832,86664762,232553036,302742306,821495496,1044549008
%N Number of geometrically distinct open knight's tours of a 3 X n chessboard that have twofold symmetry.
%D D. E. Knuth, Long and skinny knight's tours, in Selected Papers on Fun and Games, to appear, 2010.
%H 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 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 D. E. Knuth <a href="/A169770/a169770.txt">Generating functions for A169770-A169777 and A169696.</a>
%F A169776(n) = (A169773(n) + A169774(n) + A169775(n))/2.
%Y Cf. A070030, A169696, A169764-A169777.
%K nonn
%O 4,1
%A _N. J. A. Sloane_, May 10 2010, based on a communication from _Don Knuth_, Apr 28 2010
%E a(31)-a(38) from _Andrew Howroyd_, Jul 01 2017
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