OFFSET
1,2
COMMENTS
In other words, number of maximal independent vertex sets (and minimal vertex covers) in the n X n queen graph. - Eric W. Weisstein, Jun 20 2017
LINKS
S. W. Golomb and L. D. Baumert, Backtrack Programming, Journal of the ACM, 4 (2001), 516-524.
Stefan Kral, C++11 code using OpenMP
Eric Weisstein's World of Mathematics, Maximal Independent Vertex Set
Eric Weisstein's World of Mathematics, Minimal Vertex Cover
Eric Weisstein's World of Mathematics, Queen Graph
EXAMPLE
The a(2) = 4 solutions are to place a single queen in each of the squares of the chessboard. For n=3, there is a single one-queen solution (placing the queen in b2) and eight two-queen solutions, but no three-queen solution (see A000170).
CROSSREFS
KEYWORD
hard,nonn,more
AUTHOR
Paolo Bonzini, Oct 29 2008
EXTENSIONS
a(12)-a(16) from Stefan Kral, Aug 10 2016
STATUS
approved