A086900 - OEIS

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A086900

Number of real n X n symmetric (0,1) matrices with positive determinant.

1, 1, 5, 338, 14186, 526876, 52658844 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,3`
	LINKS	`Index entries for sequences related to binary matrices`
	EXAMPLE	`For n = 2 the only example is the identity matrix.`
	MATHEMATICA	`triamat[li_List] := Block[{len=Sqrt[8Length[li]+1]/2-1/2}, If[IntegerQ[len], Part[li, # ]& /@ Table[If[j>i, j(j-1)/2+i, i(i-1)/2+j], {i, len}, {j, len}], li]]; 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. A086899, A118996.` `Sequence in context: A085523 A152425 A029495 * A200002 A203684 A124477` `Adjacent sequences: A086897 A086898 A086899 * A086901 A086902 A086903`
	KEYWORD	`nonn,more`
	AUTHOR	`Wouter Meeussen (wouter.meeussen(AT)pandora.be) Aug 23, 2003.`
	EXTENSIONS	`a(6) and a(7) from Giovanni Resta (g.resta(AT)iit.cnr.it), May 08 2006`

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Last modified February 15 21:27 EST 2012. Contains 205859 sequences.