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A210905
Number of n X n 0..2 symmetric matrices with every element equal to zero or one horizontal and vertical neighbors, and new values 0..2 introduced in lower triangle row major order
0
1, 2, 24, 552, 27204, 2812168, 611509240, 279902590168, 269562004096692, 546187771866465456, 2328406266027562097220, 20883572160878878738558896, 394075725737300936910238275696
OFFSET
1,2
EXAMPLE
Some solutions for n=4
..0..1..2..0....0..1..0..1....0..1..2..2....0..1..0..2....0..1..1..0
..1..2..1..2....1..0..2..2....1..2..0..1....1..2..1..0....1..0..2..1
..2..1..0..2....0..2..1..0....2..0..0..0....0..1..0..2....1..2..2..2
..0..2..2..1....1..2..0..2....2..1..0..2....2..0..2..1....0..1..2..1
CROSSREFS
Sequence in context: A377411 A046744 A000186 * A012113 A156525 A377490
KEYWORD
nonn
AUTHOR
R. H. Hardin Mar 29 2012
STATUS
approved