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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..14.

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: A277748 A278590 A087047 * A053514 A325293 A121276

Adjacent sequences:  A211032 A211033 A211034 * A211036 A211037 A211038

KEYWORD

nonn

AUTHOR

R. H. Hardin Mar 30 2012

STATUS

approved

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Last modified September 28 16:11 EDT 2021. Contains 347716 sequences. (Running on oeis4.)