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A086812
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Number of symmetric invertible n X n matrices over GF(2).
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1
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1, 4, 28, 448, 13888, 888832, 112881664, 28897705984, 14766727757824, 15121129224011776, 30952951521552105472, 126783289432277424013312, 1038481923739784380093038592, 17014487838552627283444344291328
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| R. P. Brent and B. D. McKay, Determinants of random symmetric matrices over Zm, Ars Combinatoria, 26-A (1988) 57-64.
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LINKS
| R. P. Brent and B. D. McKay, Determinants of random symmetric matrices over Zm
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FORMULA
| Let k = ceil(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)
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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); (from Sascha Kurz)
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CROSSREFS
| Cf. A002884.
Sequence in context: A132685 A180966 A203032 * A197872 A203220 A111817
Adjacent sequences: A086809 A086810 A086811 * A086813 A086814 A086815
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KEYWORD
| nonn
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AUTHOR
| Yuval Dekel (dekelyuval(AT)hotmail.com), Sep 15 2003
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EXTENSIONS
| More terms from Ray Chandler (rayjchandler(AT)sbcglobal.net) and Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de), Sep 19 2003
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