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A211045
1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero or one horizontal and vertical neighbors
0
1, 4, 48, 1104, 54408, 5624336, 1223018480, 559805180336, 539124008193384, 1092375543732930912, 4656812532055124194440, 41767144321757757477117792
OFFSET
1,2
EXAMPLE
Some solutions for n=4
..2..1..2..2....1..0..2..0....1..2..1..2....1..0..1..2....2..0..2..1
..1..0..1..0....0..2..1..2....2..0..1..0....0..2..0..0....0..2..0..1
..2..1..0..1....2..1..1..1....1..1..2..0....1..0..2..1....2..0..1..0
..2..0..1..2....0..2..1..2....2..0..0..2....2..0..1..2....1..1..0..2
CROSSREFS
Sequence in context: A071221 A198038 A024255 * A296838 A211049 A321076
KEYWORD
nonn
AUTHOR
R. H. Hardin Mar 30 2012
STATUS
approved