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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.
2
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, 0, 0, 2087344, 0, 0, 0, 20207664, 0, 0, 0, 197082624, 0, 0, 0, 1916054112, 0, 0, 0, 18652927040, 0, 0, 0, 181485750208, 0, 0, 0, 1766199186560, 0, 0, 0
OFFSET
4,6
REFERENCES
D. E. Knuth, Long and skinny knight's tours, in Selected Papers on Fun and Games, to appear, 2010.
LINKS
George Jelliss, Open knight's tours of three-rank boards, Knight's Tour Notes, note 3a (21 October 2000).
George Jelliss, Closed knight's tours of three-rank boards, Knight's Tour Notes, note 3b (21 October 2000).
FORMULA
A169773(n)=0 unless n mod 4 = 1.
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, May 10 2010, based on a communication from Don Knuth, Apr 28 2010
EXTENSIONS
a(31)-a(60) from Andrew Howroyd, Jul 01 2017
STATUS
approved