A146049 Number of n X n binary arrays symmetric about main diagonal with all 1's connected only in a 2 X 2 block with tail 1,1 1,2 1,3 2,2 2,3 in any orientation.

1, 1, 1, 3, 13, 35, 181, 1303, 13131, 161693, 2592581, 57377381, 1720164275, 69927099465, 3715147371129, 261988046119405, 24980387570081613, 3210146525819915095, 550205755804555982181, 125514016677735094761717

Offset

1,4

Links

Table of n, a(n) for n=1..20.

Example

Maximal 8 X 8 example
.0.0.0.0.0.0.1.1
.0.0.0.0.0.0.1.1
.0.0.0.1.1.1.0.1
.0.0.1.0.1.1.0.0
.0.0.1.1.0.0.1.1
.0.0.1.1.0.0.1.1
.1.1.0.0.1.1.0.1
.1.1.1.0.1.1.1.0

Crossrefs

Sequence in context: A146741 A146725 A146424 * A061483 A340410 A128288

Adjacent sequences: A146046 A146047 A146048 * A146050 A146051 A146052

Keyword

nonn

Author

R. H. Hardin, Oct 26 2008

Status

approved