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A211047 1/3 the number of n X n 0..2 symmetric matrices with every element equal to one or two horizontal and vertical neighbors 0
0, 1, 4, 102, 3452, 306196, 56305300, 23135879808, 20936361314520, 41767961477927304, 184066448459881652770, 1789009177710334924490408 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..12.

EXAMPLE

Some solutions for n=4

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

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

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

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

CROSSREFS

Sequence in context: A129702 A220776 A180818 * A326087 A091330 A353312

Adjacent sequences:  A211044 A211045 A211046 * A211048 A211049 A211050

KEYWORD

nonn

AUTHOR

R. H. Hardin Mar 30 2012

STATUS

approved

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Last modified September 30 17:27 EDT 2022. Contains 357106 sequences. (Running on oeis4.)