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COMMENT
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Numbers of solutions to 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.
Number of perfect extremal Skolem-type sequences of order n.
Contribution from Emeric Deutsch (deutsch(AT)duke.poly.edu), Nov 28 2008: (Start)
a(n) is also the number of permutations p of {1,2,...,n} for which the numbers p(i)-i (i=1,2,...,n) are distinct. Example: a(4)=7 because we have 4132, 3142, 2413, 4213, 2431, 3241 and 4321.
a(n) is also the number of permutations p of {1,2,...,n} for which the numbers p(i)+i (i=1,2,...,n) are distinct. Example: a(4)=7 because we have 1423, 2413, 3142, 1342, 3124, 2314 and 1234.
a(n)=A125182(n,n). (End)
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