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A238923 Number of (n+1) X (1+1) 0..3 arrays with no element greater than all horizontal neighbors or equal to all vertical neighbors. 1
12, 36, 144, 540, 2052, 7776, 29484, 111780, 423792, 1606716, 6091524, 23094720, 87558732, 331960356, 1258557264, 4771552860, 18090330372, 68585649696, 260027940204, 985840769700, 3737606129712, 14170340698236, 53723840483844 (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) = 3*a(n-1) + 3*a(n-2).

Conjectures from Colin Barker, Oct 24 2018: (Start)

G.f.: 12*x / (1 - 3*x - 3*x^2).

a(n) = (-4)*(sqrt(3/7)*(((3-sqrt(21))/2)^n - ((3+sqrt(21))/2)^n)).

(End)

EXAMPLE

Some solutions for n=5:

..0..0....1..1....3..3....2..2....2..2....1..1....0..0....3..3....3..3....2..2

..3..3....2..2....2..2....0..0....1..1....0..0....1..1....1..1....1..1....3..3

..2..2....3..3....0..0....2..2....2..2....2..2....0..0....2..2....0..0....2..2

..0..0....2..2....1..1....3..3....2..2....2..2....1..1....2..2....1..1....3..3

..0..0....3..3....1..1....2..2....0..0....3..3....0..0....3..3....0..0....2..2

..2..2....1..1....0..0....0..0....1..1....1..1....3..3....0..0....1..1....1..1

CROSSREFS

Column 1 of A238929.

Sequence in context: A191817 A270840 A064518 * A135178 A278583 A216381

Adjacent sequences:  A238920 A238921 A238922 * A238924 A238925 A238926

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 07 2014

STATUS

approved

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Last modified May 19 10:36 EDT 2019. Contains 323390 sequences. (Running on oeis4.)