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A211044 1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one, two or three horizontal and vertical neighbors 1
1, 9, 216, 15444, 3281472, 2067554808, 3863711228544, 21415460458704264, 352065294244909032696, 17166897737612437082259600, 2482751631736501357900013730432, 1064995044786220639044258688726569096 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..16

EXAMPLE

Some solutions for n=4

..1..1..0..1....1..1..1..1....0..1..1..2....0..0..2..1....0..2..0..1

..1..2..2..2....1..0..2..1....1..0..1..2....0..0..2..2....2..2..1..2

..0..2..0..1....1..2..0..0....1..1..1..2....2..2..2..0....0..1..2..2

..1..2..1..0....1..1..0..1....2..2..2..2....1..2..0..2....1..2..2..2

CROSSREFS

Sequence in context: A084942 A061718 A085741 * A152288 A179153 A197669

Adjacent sequences:  A211041 A211042 A211043 * A211045 A211046 A211047

KEYWORD

nonn

AUTHOR

R. H. Hardin Mar 30 2012

STATUS

approved

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Last modified November 20 10:09 EST 2019. Contains 329334 sequences. (Running on oeis4.)