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A290280
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Number of pairs of orthogonal (diagonal, antidiagonal) X-rays for all permutations of [n].
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2
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1, 1, 2, 6, 23, 115, 674, 4718, 37371, 335435, 3340116
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OFFSET
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0,3
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COMMENTS
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The X-rays of a permutation are sequences of (diagonal, antidiagonal) sums of the corresponding permutation matrix.
A unique pair of orthogonal (diagonal, antidiagonal) X-rays allows identification of the permutation.
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LINKS
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EXAMPLE
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a(4) = 23. All permutations of {1,2,3,4} have unique pairs of orthogonal X-rays except 2413 and 3142, which share the same pair (0110110, 0110110):
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. 0110110 . 0110110
. \\\+--\-+ . \\\+--\-+
. 2 \\| 1 | . 3 \\| 1 |
. 4 \| 1| . 1 \|1 |
. 1 /|1 | . 4 /| 1|
. 3 //| 1 | . 2 //| 1 |
. ///+--/-+ . ///+--/-+
. 0110110 . 0110110
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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