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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
OFFSET
1,3
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: A304316 A377356 A186415 * A203264 A295383 A309980
KEYWORD
nonn
AUTHOR
R. H. Hardin Mar 30 2012
STATUS
approved