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A232250
Number of (n+1) X (1+1) 0..2 arrays with every element both >= and <= some horizontal or antidiagonal neighbor.
2
9, 37, 163, 723, 3209, 14245, 63235, 280707, 1246089, 5531525, 24555043, 109002515, 483874057, 2147969733, 9535072003, 42327224963, 187895169801, 834087159397, 3702603905187, 16436262714579, 72962363498889, 323887892265317
OFFSET
1,1
LINKS
FORMULA
Empirical: a(n) = 4*a(n-1) + 2*a(n-2) - a(n-4).
Empirical g.f.: x*(9 + x - 3*x^2 - 3*x^3) / (1 - 4*x - 2*x^2 + x^4). - Colin Barker, Oct 03 2018
EXAMPLE
Some solutions for n=6:
..1..1....0..0....2..2....1..1....1..1....1..1....2..2....2..2....1..1....0..0
..0..0....1..1....1..1....1..1....0..0....2..2....0..0....1..1....2..2....0..1
..2..2....2..2....2..2....0..0....0..0....1..1....0..2....1..1....2..0....1..2
..1..0....2..1....2..1....1..1....1..2....0..0....2..0....1..2....0..1....2..1
..0..0....1..2....1..2....2..2....2..0....0..0....0..0....2..2....2..2....1..0
..1..2....2..0....2..1....1..0....0..0....0..1....0..0....0..0....2..0....0..0
..2..2....0..0....1..1....0..0....1..1....2..2....0..0....0..0....0..0....0..0
CROSSREFS
Column 1 of A232257.
Sequence in context: A026620 A048878 A246315 * A201441 A183327 A364700
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 21 2013
STATUS
approved