

A211049


1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one or three horizontal and vertical neighbors


0



1, 4, 48, 1232, 69944, 8897744, 2543744944, 1632807480048, 2350761948259496, 7595900369159613200, 55087633557679363709984, 896577592582670794898595216
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OFFSET

1,2


LINKS



EXAMPLE

Some solutions for n=4
..2..0..1..2....2..0..0..2....1..0..2..2....2..1..0..2....0..2..1..0
..0..1..2..1....0..1..2..2....0..2..0..1....1..0..2..0....2..1..0..1
..1..2..0..1....0..2..1..2....2..0..1..2....0..2..1..2....1..0..2..1
..2..1..1..2....2..2..2..0....2..1..2..0....2..0..2..1....0..1..1..0


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



