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A140879
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Half the number of n X n binary matrices, symmetric about the diagonal and under 90 degree rotation, having equal row sums.
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0
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1, 1, 1, 2, 1, 5, 1, 20, 1, 139, 1, 1777, 1, 42295, 1, 1888140, 1, 158903233, 1, 25355226287, 1, 7707419775769, 1
(list; graph; refs; listen; history; internal format)
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