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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
OFFSET
1,2
CROSSREFS
Sequence in context: A280570 A080636 A223887 * A377551 A193198 A165193
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jun 18 2008
STATUS
approved