A169776 Number of geometrically distinct open knight's tours of a 3 X n chessboard that have twofold symmetry.

2, 0, 0, 2, 10, 12, 22, 60, 76, 160, 292, 652, 1148, 2600, 3870, 9152, 13710, 32792, 48112, 116624, 171732, 428064, 589842, 1496508, 2069766, 5348640, 7164172, 18742712, 25160796, 66758832, 86664762, 232553036, 302742306, 821495496, 1044549008

Offset: 4

Author

N. J. A. Sloane, May 10 2010, based on a communication from Don Knuth, Apr 28 2010

Keywords

• nonn

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).
• D. E. Knuth Generating functions for A169770-A169777 and A169696.

Crossrefs

Cf. A070030, A169696, A169764-A169777.

Formula

A169776(n) = (A169773(n) + A169774(n) + A169775(n))/2.

Extensions

a(31)-a(38) from Andrew Howroyd, Jul 01 2017