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A145939 Number of n X n binary arrays symmetric about both diagonal and antidiagonal with all ones connected only in a 2X2 elbow 1,1 1,2 2,1 in any orientation. 0
1, 1, 3, 5, 15, 39, 133, 511, 2773, 14873, 106373, 810293, 8275081, 88902809, 1280398135, 19384764865, 392921704943, 8381650583597, 239524090999801, 7208159770278487, 290528855860261289, 12317566856380616673 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..22.

EXAMPLE

Maximal 8 X 8 example

.0.1.1.0.1.0.1.1

.1.0.1.0.1.1.0.1

.1.1.0.1.0.0.1.0

.0.0.1.1.0.0.1.1

.1.1.0.0.1.1.0.0

.0.1.0.0.1.0.1.1

.1.0.1.1.0.1.0.1

.1.1.0.1.0.1.1.0

CROSSREFS

Sequence in context: A280764 A148503 A236571 * A161703 A018551 A103425

Adjacent sequences:  A145936 A145937 A145938 * A145940 A145941 A145942

KEYWORD

nonn

AUTHOR

R. H. Hardin, Oct 25 2008

STATUS

approved

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Last modified January 29 08:04 EST 2020. Contains 331337 sequences. (Running on oeis4.)