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 A086899 Number of real n X n invertible symmetric (0,1) matrices. 5
 1, 4, 32, 528, 18596, 1280468, 180452552 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Table of n, a(n) for n=1..7. Index entries for sequences related to binary matrices EXAMPLE For n = 2 the 4 matrices are 10/01, 01/10, 11/10, 01/11. MATHEMATICA 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}] CROSSREFS Cf. A086900, A086906, A118991. Sequence in context: A127945 A036442 A186339 * A219149 A013041 A006024 Adjacent sequences: A086896 A086897 A086898 * A086900 A086901 A086902 KEYWORD nonn,more AUTHOR Wouter Meeussen Aug 23, 2003. EXTENSIONS a(6) and a(7) from Giovanni Resta, May 08 2006 STATUS approved

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Last modified June 12 18:04 EDT 2024. Contains 373359 sequences. (Running on oeis4.)