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A211040 1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one or three horizontal and vertical neighbors 0
1, 4, 40, 928, 45128, 4945168, 1207742160, 655725571768, 791701825710768, 2127149017683661104, 12717092443922120808584, 169157473880575759274475472, 5006302388939519643670779061032 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..13.

EXAMPLE

Some solutions for n=4

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

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

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

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

CROSSREFS

Sequence in context: A055128 A117251 A220404 * A012957 A012977 A321526

Adjacent sequences: A211037 A211038 A211039 * A211041 A211042 A211043

KEYWORD

nonn

AUTHOR

R. H. Hardin Mar 30 2012

STATUS

approved

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Last modified December 8 14:04 EST 2022. Contains 358693 sequences. (Running on oeis4.)