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 A086812 Number of symmetric invertible n X n matrices over GF(2). 1
 1, 4, 28, 448, 13888, 888832, 112881664, 28897705984, 14766727757824, 15121129224011776, 30952951521552105472, 126783289432277424013312, 1038481923739784380093038592, 17014487838552627283444344291328 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES R. P. Brent and B. D. McKay, Determinants of random symmetric matrices over Zm, Ars Combinatoria, 26-A (1988) 57-64. LINKS Table of n, a(n) for n=1..14. R. P. Brent and B. D. McKay, Determinants of random symmetric matrices over Zm, arXiv:1004.5440 [math.CO], 2010. FORMULA Let k = ceiling(n/2). Then a(n) = 2^(n*(n+1)/2) * (Product_{j=1..2k} (1 - (1/2)^j)) / Product_{j=1..k} (1 - (1/4)^j). MAPLE for n from 1 to 31 do k := ceil(n/2); a[n] := 2^(n*(n+1)/2)*product(1-(1/2)^j, j=1..2*k)/product(1-(1/4)^j, j=1..k); od:seq(a[j], j=1..31); # Sascha Kurz, Sep 19 2003 MATHEMATICA m = 14; For[n = 1, n <= m, n++, k = Ceiling[n/2]; a[n] = 2^(n*(n+1)/2)* Product[1-(1/2)^j, {j, 1, 2k}]/Product[1-(1/4)^j, {j, 1, k}]]; Array[a, m] (* Jean-François Alcover, Feb 24 2019, from Maple *) CROSSREFS Cf. A002884. Sequence in context: A132685 A180966 A203032 * A197872 A203220 A338816 Adjacent sequences: A086809 A086810 A086811 * A086813 A086814 A086815 KEYWORD nonn AUTHOR Yuval Dekel (dekelyuval(AT)hotmail.com), Sep 15 2003 EXTENSIONS More terms from Ray Chandler and Sascha Kurz, Sep 19 2003 STATUS approved

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Last modified July 14 13:00 EDT 2024. Contains 374318 sequences. (Running on oeis4.)