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A333164
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Number of 2n X 2n symmetric matrices with entries in {+1, -1} and all rows and columns summing to zero.
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4
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1, 2, 18, 1760, 1944530, 26615510712, 4762109992158288, 11528251571501588791296, 386860001875783390762182911250, 183238648400953515891207813311894423000, 1242327573587456839123512395835593196519781229768, 121917941188016997420391711911475819481799846311888884541952
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OFFSET
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0,2
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COMMENTS
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a(n) is the number of 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) = 2 matrices are:
[ 1 -1] [-1 1]
[-1 1] [ 1 -1]
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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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