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A211038 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, 72, 2088, 148758, 21763840, 7132571384, 5048293367644, 7844581606488974, 26582841246234004080, 197025807090354544802766 (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

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

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

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

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

CROSSREFS

Sequence in context: A176901 A304316 A186415 * A203264 A295383 A309980

Adjacent sequences: A211035 A211036 A211037 * A211039 A211040 A211041

KEYWORD

nonn

AUTHOR

R. H. Hardin Mar 30 2012

STATUS

approved

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Last modified November 29 18:13 EST 2022. Contains 358431 sequences. (Running on oeis4.)