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A210902
Number of n X n 0..2 symmetric matrices with every element equal to zero, two or three horizontal and vertical neighbors, and new values 0..2 introduced in lower triangle row major order
0
1, 3, 17, 252, 6328, 297609, 25886499, 4205102578, 1265408306700, 707818003940086, 733897633220152333, 1410044723992401143016
OFFSET
1,2
EXAMPLE
Some solutions for n=4
..0..1..2..0....0..0..0..0....0..1..0..0....0..1..2..2....0..1..2..1
..1..2..0..1....0..1..0..0....1..2..0..0....1..0..2..2....1..0..1..0
..2..0..2..0....0..0..1..0....0..0..1..0....2..2..0..1....2..1..2..1
..0..1..0..1....0..0..0..0....0..0..0..0....2..2..1..2....1..0..1..0
CROSSREFS
Sequence in context: A322737 A376008 A201107 * A188803 A084040 A009495
KEYWORD
nonn
AUTHOR
R. H. Hardin Mar 29 2012
STATUS
approved