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A328341 Number of geometrically distinct open knight's tours on a 4 X n chessboard.

%I A328341 #7 Oct 13 2019 18:14:00
%S A328341 0,0,3,0,22,186,1603,7772,47478,303278,1671273,9121582,50322028,
%T A328341 270896326,1426536267,7454807822,38607660199,197696949844,
%U A328341 1003736587788,5060326202622,25334034892953,126024078250318,623383415637750,3067618264121349,15022847233751804,73245459228339114
%N A328341 Number of geometrically distinct open knight's tours on a 4 X n chessboard.
%H A328341 George Jellis, <a href="http://www.mayhematics.com/t/oc.htm">Knight's tours of Four Rank Boards</a>
%F A328341 a(2*n) = A123936(2*n)/2; a(2*n-1) = (A123936(2*n-1) + A328340(n))/2.
%e A328341 a(3) = 3 because there are two symmetric and one asymmetric tour:
%e A328341   +----+----+----+----+   +----+----+----+----+   +----+----+----+----+
%e A328341   |  8 | 11 |  6 |  3 |   |  1 |  4 |  7 | 10 |   |  1 |  4 |  7 | 10 |
%e A328341   +----+----+----+----+   +----+----+----+----+   +----+----+----+----+
%e A328341   |  1 |  4 |  9 | 12 |   |  8 | 11 |  2 |  5 |   | 12 |  9 |  2 |  5 |
%e A328341   +----+----+----+----+   +----+----+----+----+   +----+----+----+----+
%e A328341   | 10 |  7 |  2 |  5 |   |  3 |  6 |  9 | 12 |   |  3 |  6 | 11 |  8 |
%e A328341   +----+----+----+----+   +----+----+----+----+   +----+----+----+----+
%Y A328341 Cf. A079137, A123936, A169777, A328340.
%K A328341 nonn
%O A328341 1,3
%A A328341 _Andrew Howroyd_, Oct 12 2019