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A211077
1/4 the number of n X n 0..3 symmetric matrices with every element equal to zero or one horizontal and vertical neighbors
1
1, 9, 297, 30213, 9904329, 10357083063, 34636341072699, 370225462363917579, 12650055630492583306593, 1381655999590131944779825905, 482381759955085135355798493794163
OFFSET
1,2
LINKS
EXAMPLE
Some solutions for n=4
..0..3..2..3....0..1..2..1....1..0..2..2....3..0..1..0....2..3..0..3
..3..1..0..1....1..3..0..1....0..1..3..1....0..2..1..3....3..2..1..1
..2..0..2..0....2..0..2..3....2..3..0..1....1..1..3..2....0..1..3..0
..3..1..0..1....1..1..3..0....2..1..1..2....0..3..2..0....3..1..0..1
CROSSREFS
Sequence in context: A371252 A012838 A216966 * A211082 A061685 A183549
KEYWORD
nonn
AUTHOR
R. H. Hardin Mar 31 2012
STATUS
approved