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A211080
1/4 the number of n X n 0..3 symmetric matrices with every element equal to one or two horizontal and vertical neighbors.
0
0, 1, 6, 276, 19788, 4909014, 2929172742, 5071671459180, 23339078849741382, 298199841357475363224
OFFSET
1,3
EXAMPLE
Some solutions for n=4
..3..3..2..2....3..3..3..3....1..1..0..0....3..3..2..2....0..0..2..2
..3..3..1..2....3..1..1..1....1..1..3..1....3..3..0..1....0..0..1..1
..2..1..1..0....3..1..0..0....0..3..3..1....2..0..0..1....2..1..0..0
..2..2..0..0....3..1..0..0....0..1..1..1....2..1..1..1....2..1..0..0
CROSSREFS
Sequence in context: A250390 A284071 A254628 * A288796 A199097 A342983
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 31 2012
STATUS
approved