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A239171 Number of (n+1) X (1+1) 0..2 arrays with no element greater than all horizontal neighbors or equal to all vertical neighbors. 1
6, 12, 36, 96, 264, 720, 1968, 5376, 14688, 40128, 109632, 299520, 818304, 2235648, 6107904, 16687104, 45590016, 124554240, 340288512, 929685504, 2539948032, 6939267072, 18958430208, 51795394560, 141507649536, 386606088192 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

FORMULA

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

Conjectures from Colin Barker, Oct 25 2018: (Start)

G.f.: 6*x / (1 - 2*x - 2*x^2).

a(n) = sqrt(3)*((1+sqrt(3))^n-(1-sqrt(3))^n).

(End)

EXAMPLE

Some solutions for n=5:

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

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

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

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

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

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

CROSSREFS

Column 1 of A239178.

Sequence in context: A176681 A064476 A324483 * A264955 A038266 A298881

Adjacent sequences:  A239168 A239169 A239170 * A239172 A239173 A239174

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 11 2014

STATUS

approved

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Last modified August 18 06:42 EDT 2019. Contains 326072 sequences. (Running on oeis4.)