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A140425 Number of n X n symmetric binary matrices with every 1 adjacent to another 1 horizontally or vertically. 0
1, 4, 28, 342, 8170, 388316, 35871274, 6434968504, 2248575047080, 1530856226085764, 2029777404349820818, 5241143888167535563974, 26356732501074298121803368, 258136468277025366420232101764 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..14.

CROSSREFS

Sequence in context: A113371 A080636 A223887 * A193198 A165193 A217903

Adjacent sequences:  A140422 A140423 A140424 * A140426 A140427 A140428

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jun 18 2008

STATUS

approved

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Last modified December 17 19:18 EST 2014. Contains 252038 sequences.