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A211039
1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one or two horizontal and vertical neighbors.
0
1, 9, 204, 12780, 2172082, 1005151346, 1266392434410, 4344083373089662, 40572956283401922254, 1031771738712216572967968, 71439807978713378989930266486, 13468111519258747911321811422788604
OFFSET
1,2
EXAMPLE
Some solutions for n=4
..1..1..2..1....2..0..1..0....1..2..0..1....2..0..0..2....1..2..0..1
..1..1..2..1....0..2..2..2....2..2..1..2....0..2..0..0....2..1..0..2
..2..2..0..1....1..2..0..1....0..1..1..2....0..0..2..2....0..0..1..1
..1..1..1..1....0..2..1..1....1..2..2..2....2..0..2..2....1..2..1..2
CROSSREFS
Sequence in context: A012108 A251587 A103914 * A307735 A266483 A203364
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 30 2012
STATUS
approved