A211048 - OEIS

A211048

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

1, 9, 226, 15556, 2941772, 1527584784, 2177623382864, 8522206940566808, 91558683282725300624, 2700384338082047133898512, 218639776300578162500042598232, 48597088081320286927152305357894272, 29653005976460334510836491437647123258008

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OFFSET

1,2

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..13

EXAMPLE

Some solutions for n=4:

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

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

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

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

CROSSREFS

Sequence in context: A330830 A218536 A338377 * A327146 A158728 A197406

Adjacent sequences: A211045 A211046 A211047 * A211049 A211050 A211051

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 30 2012

EXTENSIONS

Name corrected by Andrew Howroyd, Mar 25 2025

STATUS

approved