n-queens problem: a modified version
From: Simone Severini (ss54_at_york.ac.uk)
Date: 11/18/04
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Date: 18 Nov 2004 14:58:51 -0500
Dear All,
The n-queens problem asks in how many ways we can put n queens in an n
by n chess board such that no two queens attack each other.
Look at the following problem:
What is the number of n by n permutation matrices whose sums of the
entries of each NorthEast-SouthWest diagonal are 0 or 1?
This is a modified version of the n-queens problem, in which two
queens do not attack each other if they are in the same
NorthWest-SouthEst diagonal.
(unless I made mistakes) The related integer sequence is
1,1,3,7,23,83,405,2113,12657,82297,...
http://www.research.att.com/cgi-bin/access.cgi/as/njas/sequences/eisA.cgi?Anum=A099152
Do you have any clou about a formula for this sequence?
Cheers,
Simone Severini
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