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A211043
1/3 the number of n X n 0..2 symmetric matrices with every element equal to one, two or three horizontal and vertical neighbors.
0
0, 1, 8, 156, 7480, 898680, 266674964, 196750879896, 360466213243792, 1640421325318165822, 18541481770815952051304, 520535380394250894532873968, 36296751650483051319011293939152
OFFSET
1,3
EXAMPLE
Some solutions for n=4
..2..2..1..1....1..1..0..1....0..0..1..2....2..2..1..1....2..2..1..1
..2..2..1..0....1..0..0..1....0..1..1..2....2..2..0..2....2..1..1..1
..1..1..1..0....0..0..2..2....1..1..2..2....1..0..0..2....1..1..0..0
..1..0..0..0....1..1..2..2....2..2..2..2....1..2..2..2....1..1..0..0
CROSSREFS
Sequence in context: A251586 A221098 A171211 * A025605 A114223 A278669
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 30 2012
STATUS
approved