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A191508 Number of n X n symmetric binary matrices with each 1 adjacent to no more than 3 horizontally or vertically neighboring 1s 1
2, 8, 56, 792, 21984, 1188160, 125522112, 25932064896, 10472077118464, 8266074697979136, 12754433913314441216, 38469498012053658897408, 226810241439860068417249280, 2613967215944945112514234085376 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..25

EXAMPLE

Some solutions for n=4

..0..1..0..0....0..0..1..1....0..0..0..1....0..0..0..1....1..0..0..0

..1..0..1..0....0..0..0..1....0..0..0..1....0..1..1..1....0..0..1..0

..0..1..0..1....1..0..0..0....0..0..0..1....0..1..1..0....0..1..0..0

..0..0..1..1....1..1..0..1....1..1..1..0....1..1..0..1....0..0..0..0

CROSSREFS

Sequence in context: A084872 A254231 A191713 * A113725 A256724 A153538

Adjacent sequences:  A191505 A191506 A191507 * A191509 A191510 A191511

KEYWORD

nonn

AUTHOR

R. H. Hardin Jun 04 2011

STATUS

approved

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Last modified October 27 23:26 EDT 2020. Contains 338047 sequences. (Running on oeis4.)