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Eight queens puzzle - Wikipedia -- place eight chess queens on a chessboard so that none of them attack each other.

It turns out that there are 92 solutions, though when one counts together positions related by chessboard symmetries, there are only 12 solutions.

This problem has been modified and extended in a variety of ways.

It turns out that there are 92 solutions, though when one counts together positions related by chessboard symmetries, there are only 12 solutions.

This problem has been modified and extended in a variety of ways.

**Different-sized boards.**The problem has been solved for board sizes up to 27. No formula is known for the number of solutions, not even its asymptotic behavior. But the size appears to increase factorially.**Different board geometries.**This problem has been studied for periodic boundary conditions: toroidal topology.**Different numbers of dimensions.**This problem has been studied for cubical boards and higher-dimensional ones.**Different chess pieces.**This problem has been solved or at least studied for rooks (max n), bishops (max 2(n-1)), knights, and kings. Also for "fairy chess" pieces with different kinds of moves from the canonical pieces' moves.
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