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A211035
1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero or one horizontal or vertical neighbor
0
1, 4, 40, 800, 33432, 2888696, 517902680, 192533704008, 148429379845856, 237284500891487840, 786611979025079107456, 5407447771030956200932952, 77084070831919712319047890192, 2278648745820732735808198902023640
OFFSET
1,2
EXAMPLE
Some solutions for n=4
..1..0..2..2....2..1..0..0....0..1..0..2....0..1..1..0....1..2..1..0
..0..1..0..0....1..0..2..1....1..2..0..2....1..2..0..2....2..0..1..2
..2..0..1..2....0..2..0..2....0..0..2..0....1..0..2..0....1..1..0..1
..2..0..2..1....0..1..2..0....2..2..0..1....0..2..0..1....0..2..1..0
CROSSREFS
Sequence in context: A278590 A370086 A087047 * A053514 A325293 A121276
KEYWORD
nonn
AUTHOR
R. H. Hardin Mar 30 2012
STATUS
approved