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A140884
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Half the number of n X n binary matrices, symmetric under 90-degree rotation, having equal row sums.
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0
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1, 1, 1, 4, 3, 13, 43, 580, 1897, 23851, 149041, 14348161, 74552521, 7849966951, 311500453881, 64690704744716, 2466747100788601, 493809829542170401
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OFFSET
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1,4
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LINKS
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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