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%I #26 Oct 27 2019 21:31:38
%S 0,5,0,2,149,49,1,12897,2238
%N Consider problem of placing N queens on an n X n board so that each queen attacks precisely k others. Here k=1 and sequence gives number of inequivalent solutions when N is equal to the upper bound 2*floor(2n/3).
%C a(n) = 0 if N does not achieve 2*floor(2n/3).
%D M. Gardner, The Last Recreations, Springer, 1997, p. 282.
%D M. Gardner, The Colossal Book of Mathematics, 2001, p. 209.
%H Martin Gardner, <a href="http://www.scribd.com/doc/207185086/Gardner-1997-the-Last-Recreations">The Last Recreations</a>, 1997
%H Vaclav Kotesovec, <a href="/A051567/a051567.jpg">The unique solution for chessboard 9 X 9</a>
%H Manfred Scheucher, <a href="/A051567/a051567.c.txt">C Code</a>
%Y Cf. A051568-A051571, A051754-A051759, A019654.
%Y The number of solutions when N takes its maximal value is A051757.
%K nonn,more,nice
%O 3,2
%A _N. J. A. Sloane_
%E Description corrected by and one more term from _Jud McCranie_, Aug 25 2001
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