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A145861 Number of n X n binary arrays symmetric about both diagonal and antidiagonal with all ones connected only in two by two blocks. 0
1, 2, 1, 4, 4, 13, 13, 58, 68, 386, 540, 3520, 6019, 47375, 94643, 905453, 2187052, 24871767, 71992142, 980875049, 3393779522, 55564082030, 230467066626, 4514573141799, 22448445351838, 526789383889476, 3136759423470421 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..27.

EXAMPLE

Maximal 7 X 7 example

.1.1.0.1.1.0.0

.1.1.0.1.1.0.0

.0.0.0.0.0.1.1

.1.1.0.0.0.1.1

.1.1.0.0.0.0.0

.0.0.1.1.0.1.1

.0.0.1.1.0.1.1

CROSSREFS

Sequence in context: A048049 A212716 A057772 * A191660 A129874 A021983

Adjacent sequences:  A145858 A145859 A145860 * A145862 A145863 A145864

KEYWORD

nonn

AUTHOR

R. H. Hardin, Oct 22 2008

STATUS

approved

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Last modified August 8 18:36 EDT 2020. Contains 336298 sequences. (Running on oeis4.)