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A086899 Number of real n X n invertible symmetric (0,1) matrices. 5
1, 4, 32, 528, 18596, 1280468, 180452552 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 20 07:17 EDT 2018. Contains 316378 sequences. (Running on oeis4.)