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In how many different ways can k bishops be placed on an nxn chessboard such that no two bishops attack each other? Please try to respond with a formula and explanation.

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A quick pointer in the right direction: you want "rook polynomials" (, calculated separately for black squares and white squares, and then recombined somehow. Also, this is not "combinatorial game theory" as that term is usually understood; I'll remove the tag. – Michael Lugo Feb 7 '11 at 18:27
up vote 22 down vote accepted

Call this number $B_k(n)$. For fixed $k$ it is known that $B_k(n)$ has the form $P_k(n)+(-1)^nQ_k(n)$, where $P_k$ and $Q_k$ are polynomials. These polynomials have been computed for (at least) $k\leq 6$. We also have (unsurprisingly) the asymptotic formula $B_k(n)\sim n^{2k}/k!$. For further information see

Update. I learned from Tom Zaslavsky that an explicit formula for $B_k(n)$ as a triple sum was given by C. E. Arshon in 1936.

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Special thanks for the link. – fnasim Feb 7 '11 at 19:02

See my book , page 234-236. Number of ways to place k non-attacking bishops on an n x n board, (n>1)

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