A086899 - OEIS

A086899

Number of real n X n invertible symmetric (0,1) matrices.

1, 4, 32, 528, 18596, 1280468, 180452552

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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