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A086899
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Number of real n X n invertible symmetric (0,1) matrices.
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5
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OFFSET
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1,2
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LINKS
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EXAMPLE
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For n = 2 the 4 matrices are 10/01, 01/10, 11/10, 01/11.
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MATHEMATICA
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triamat[li_List] := (*see A086900*); Table[it=triamat/@IntegerDigits[Range[0, -1+2^(n(n+1)/2)], 2, n(n+1)/2]; Count[it, (q_)?MatrixQ/; (Det[q]=!=0)], {n, 5}]
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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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EXTENSIONS
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STATUS
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approved
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