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A141512 Number of n X n binary matrices, symmetric about the diagonal and under 90 degree rotation, with no more than 3 ones in any 2 X 2 subblock. 1
1, 2, 1, 7, 4, 49, 21, 648, 245, 16475, 5184, 801489, 214175, 74700792, 16831269, 13333992705, 2539826928, 4558747755857, 733369598775, 2985167883475040, 405728550271273, 3743977846899435969, 429864175220405760 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

R. H. Hardin, Table of n, a(n) for n = 0..30

CROSSREFS

Sequence in context: A087059 A120872 A204771 * A143877 A019642 A248811

Adjacent sequences:  A141509 A141510 A141511 * A141513 A141514 A141515

KEYWORD

nonn

AUTHOR

R. H. Hardin, Aug 10 2008

STATUS

approved

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Last modified December 4 11:13 EST 2016. Contains 278750 sequences.