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A213434 Number of n X n symmetric binary matrices with zero diagonal and no three-node loops x(i,j)*x(j,k)*x(k,i) = 1, i < j < k. 0
1, 2, 7, 41, 388, 5789, 133501, 4682270, 246348115, 19213627145, 2198376297964, 365587270414697, 87628189849380625 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Equivalently, number of triangle-free labeled graphs on n vertices. - Falk Hüffner, Jun 19 2018

LINKS

Table of n, a(n) for n=1..13.

F. Hüffner, tinygraph, software for generating integer sequences based on graph properties, version 8c665c7

EXAMPLE

Some solutions for n=4:

  0 1 0 0     0 1 1 0     0 1 0 0     0 0 1 1     0 1 0 0

  1 0 1 0     1 0 0 1     1 0 0 0     0 0 1 0     1 0 0 1

  0 1 0 1     1 0 0 1     0 0 0 1     1 1 0 0     0 0 0 0

  0 0 1 0     0 1 1 0     0 0 1 0     1 0 0 0     0 1 0 0

CROSSREFS

Sequence in context: A047864 A173916 A163921 * A008934 A084871 A122942

Adjacent sequences:  A213431 A213432 A213433 * A213435 A213436 A213437

KEYWORD

nonn,more

AUTHOR

R. H. Hardin, Jun 11 2012

EXTENSIONS

a(11)-a(13) added using tinygraph by Falk Hüffner, Jun 19 2018

STATUS

approved

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Last modified February 16 12:48 EST 2019. Contains 320163 sequences. (Running on oeis4.)