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A333165
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Number of non-isomorphic 2n X 2n symmetric matrices with entries in {+1, -1} and all rows and columns summing to zero.
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3
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1, 1, 2, 5, 66, 7937, 10211144, 133506398361, 18551599312980440, 28652629505982770906471, 510824181488832447063505273252
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OFFSET
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0,3
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COMMENTS
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a(n) is the number of non-isomorphic 2n X 2n symmetric binary matrices with n ones in every row and column.
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LINKS
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FORMULA
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EXAMPLE
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The a(1) = 1 matrix is:
[+ -]
[- +]
The a(2) = 2 matrices are:
[+ + - -] [+ + - -]
[+ + - -] [+ - + -]
[- - + +] [- + - +]
[- - + +] [- - + +]
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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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