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A210921 Number of n X n 0..3 symmetric matrices with every element equal to zero or two horizontal and vertical neighbors, and new values 0..3 introduced in lower triangle row major order. 0
1, 3, 39, 2107, 277902, 87883641, 66460660741, 120226326939778, 520179215730042235, 5383068220104980704743, 133236771262960489496028245 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..11.

EXAMPLE

Some solutions for n=4

..0..1..0..3....0..0..1..1....0..1..1..1....0..1..0..1....0..1..2..3

..1..2..1..2....0..0..1..1....1..1..0..1....1..0..1..2....1..0..3..1

..0..1..2..3....1..1..2..0....1..0..1..1....0..1..2..0....2..3..0..0

..3..2..3..1....1..1..0..1....1..1..1..2....1..2..0..2....3..1..0..0

CROSSREFS

Sequence in context: A084881 A193122 A015017 * A290516 A210925 A300046

Adjacent sequences: A210918 A210919 A210920 * A210922 A210923 A210924

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 29 2012

STATUS

approved

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Last modified February 4 22:05 EST 2023. Contains 360082 sequences. (Running on oeis4.)