A231025 - OEIS

A231025

Number of n X 2 0..2 arrays x(i,j) with each element horizontally, vertically or antidiagonally next to at least one element with value (x(i,j)+1) mod 3 and at least one element with value (x(i,j)-1) mod 3, and upper left element zero.

0, 2, 12, 62, 344, 1864, 10162, 55324, 301278, 1640592, 8933808, 48648834, 264916012, 1442593630, 7855607976, 42777519416, 232943926258, 1268490401852, 6907533179198, 37614801461920, 204830473095648, 1115399286396802

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OFFSET

1,2

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..210

FORMULA

Empirical: a(n) = 4*a(n-1) + 8*a(n-2) - 4*a(n-4) + a(n-5).

Empirical g.f.: 2*x^2*(1 + 2*x - x^2) / (1 - 4*x - 8*x^2 + 4*x^4 - x^5). - Colin Barker, Sep 25 2018

EXAMPLE

Some solutions for n=3:

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

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

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

CROSSREFS

Column 2 of A231031.

Sequence in context: A226506 A026076 A361812 * A330387 A368760 A272363

Adjacent sequences: A231022 A231023 A231024 * A231026 A231027 A231028

KEYWORD

nonn

AUTHOR

R. H. Hardin, Nov 03 2013

STATUS

approved