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A141505 Number of n X n binary matrices, symmetric about both diagonal and antidiagonal, with no more than 2 ones in any 2 X 2 subblock. 0
1, 2, 3, 9, 21, 113, 469, 4085, 28379, 421721, 4946881, 123415785, 2438547133, 102642272877, 3418605422546, 242398759656743, 13604569959521965, 1625856487869820237, 153782502309772183952, 30970307573051859177121, 4936590429632104565792997, 1675450994355334964940357075 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..21.

CROSSREFS

Sequence in context: A301809 A056780 A324614 * A111360 A111238 A057832

Adjacent sequences:  A141502 A141503 A141504 * A141506 A141507 A141508

KEYWORD

nonn

AUTHOR

R. H. Hardin, Aug 10 2008

STATUS

approved

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Last modified May 28 04:00 EDT 2020. Contains 334671 sequences. (Running on oeis4.)