A210905 - OEIS

A210905

Number of n X n 0..2 symmetric matrices with every element equal to zero, one or four horizontal and vertical neighbors, and new values 0..2 introduced in lower triangle row major order.

1, 2, 24, 552, 27204, 2812168, 611509240, 279902590168, 269562004096692, 546187771866465456, 2328406266027562097220, 20883572160878878738558896, 394075725737300936910238275696

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OFFSET

1,2

LINKS

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

EXAMPLE

Some solutions for n=4:

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

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

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

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

CROSSREFS

Sequence in context: A377411 A046744 A000186 * A012113 A156525 A393751

Adjacent sequences: A210902 A210903 A210904 * A210906 A210907 A210908

KEYWORD

nonn,more

AUTHOR

R. H. Hardin, Mar 29 2012

EXTENSIONS

Name corrected by Andrew Howroyd, Mar 25 2025

STATUS

approved