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A211087
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, 324, 35343, 12487068, 14118092100, 51199696832895, 595365272306224965, 22199455509688700548632, 2654252181204304007637930258, 1017614219466672806577892453493568
OFFSET
1,2
LINKS
EXAMPLE
Some solutions for n=4
..1..3..0..1....3..0..2..3....3..0..2..0....1..3..1..3....0..3..3..0
..3..1..2..1....0..2..0..0....0..1..0..3....3..3..3..2....3..1..2..1
..0..2..2..2....2..0..2..1....2..0..2..3....1..3..1..0....3..2..3..1
..1..1..2..0....3..0..1..3....0..3..3..2....3..2..0..1....0..1..1..0
CROSSREFS
Sequence in context: A156634 A128788 A164080 * A211091 A124070 A203763
KEYWORD
nonn
AUTHOR
R. H. Hardin Mar 31 2012
STATUS
approved