A086900 Number of real n X n symmetric (0,1) matrices with positive determinant.

1, 1, 5, 338, 14186, 526876, 52658844

Offset

1,3

Links

Table of n, a(n) for n=1..7.

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: A316128 A317434 A029495 * A200002 A265921 A203684

Adjacent sequences: A086897 A086898 A086899 * A086901 A086902 A086903

Keyword

nonn,more

Author

Wouter Meeussen Aug 23, 2003.

Extensions

a(6) and a(7) from Giovanni Resta, May 08 2006

Status

approved