A140425 Number of n X n symmetric binary matrices with every 1 adjacent to another 1 horizontally or vertically.

1, 4, 28, 342, 8170, 388316, 35871274, 6434968504, 2248575047080, 1530856226085764, 2029777404349820818, 5241143888167535563974, 26356732501074298121803368, 258136468277025366420232101764

Offset

1,2

Links

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

Crossrefs

Sequence in context: A280570 A080636 A223887 * A377551 A193198 A165193

Adjacent sequences: A140422 A140423 A140424 * A140426 A140427 A140428

Keyword

nonn

Author

R. H. Hardin, Jun 18 2008

Status

approved