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A232508
Number of (n+1) X (1+1) 0..2 arrays with every element next to itself plus and minus one within the range 0..2 horizontally, diagonally or antidiagonally, with no adjacent elements equal.
1
4, 4, 8, 16, 28, 52, 96, 176, 324, 596, 1096, 2016, 3708, 6820, 12544, 23072, 42436, 78052, 143560, 264048, 485660, 893268, 1642976, 3021904, 5558148, 10223028, 18803080, 34584256, 63610364, 116997700, 215192320, 395800384, 727990404
OFFSET
1,1
LINKS
FORMULA
Empirical: a(n) = a(n-1) + a(n-2) + a(n-3).
Empirical g.f.: 4*x / (1 - x - x^2 - x^3). - Colin Barker, Oct 05 2018
EXAMPLE
Some solutions for n=7:
..1..0....0..1....1..0....1..0....0..1....2..1....0..1....1..0....0..1....0..1
..1..2....2..1....1..2....1..2....2..1....0..1....2..1....1..2....2..1....2..1
..1..0....2..1....1..0....1..0....2..0....0..1....2..1....1..2....0..1....0..1
..1..2....0..1....1..2....1..2....1..0....2..1....0..1....1..0....2..1....0..2
..1..0....2..1....1..0....1..2....1..2....0..1....0..1....1..0....2..1....1..2
..1..2....0..1....1..2....1..0....1..2....0..1....2..1....1..2....0..1....1..0
..1..2....0..1....1..0....1..0....1..0....2..1....0..1....1..0....2..1....1..0
..1..0....2..1....1..2....1..2....1..2....0..1....2..1....1..2....0..1....1..2
CROSSREFS
Column 1 of A232515.
Sequence in context: A030168 A261212 A112435 * A028610 A019171 A038551
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 25 2013
STATUS
approved