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A211041
1/3 the number of n X n 0..2 symmetric matrices with every element equal to two or three horizontal and vertical neighbors.
0
0, 1, 0, 6, 8, 118, 880, 14400, 318220, 10446298, 531060152, 39577654480, 4465022457276, 757302604610482, 191605833481050984
OFFSET
1,4
EXAMPLE
Some solutions for n=4
..0..0..1..1....0..0..1..1....2..2..0..0....2..2..1..1....1..1..1..1
..0..0..1..1....0..0..1..1....2..2..0..0....2..2..1..1....1..2..2..1
..1..1..0..0....1..1..2..2....0..0..1..1....1..1..2..2....1..2..2..1
..1..1..0..0....1..1..2..2....0..0..1..1....1..1..2..2....1..1..1..1
CROSSREFS
Sequence in context: A013234 A013240 A161801 * A236754 A069660 A119001
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 30 2012
STATUS
approved