|
%I #19 May 23 2014 00:40:44
%S 4,2,1,1,5,2,15,3
%N Let M(n) (A051755) be the maximal number of queens that can be placed on an n X n chessboard so that each queen attacks exactly two other queens; a(n) is the number of non-equivalent solutions. "Non-equivalent" means none of the a(n) solutions can be mapped onto any other solution by board rotations through 90, 180 or 270 degrees or mirror operations along the two diagonals or center lines.
%D M. Gardner, The Last Recreations, Springer, 1997, p. 282.
%D M. Gardner, The Colossal Book of Mathematics, 2001, p. 209.
%H Ken Duisenberg, <a href="http://ken.duisenberg.com/potw/archive/arch00/000628.html">Doubly Attacking Queens, POTW 2000</a>.
%Y Cf. A051567-A051571, A051754-A051759, A019654.
%K nonn,nice,more
%O 3,1
%A _N. J. A. Sloane_, Dec 11 1999
%E More precise definition from _R. J. Mathar_, Mar 13 2006
%E Edited by _N. J. A. Sloane_, May 22 2014
|
