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A184041 1/9 the number of (n+1) X 3 0..2 arrays with all 2 X 2 subblocks having the same four values. 1
15, 21, 31, 51, 87, 159, 295, 567, 1095, 2151, 4231, 8391, 16647, 33159, 66055, 131847, 263175, 525831, 1050631, 2100231, 4198407, 8394759, 16785415, 33566727, 67125255, 134242311, 268468231, 536920071, 1073807367, 2147581959, 4295098375 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 2 of A184048.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..200

FORMULA

Empirical: a(n) = 3*a(n-1) - 6*a(n-3) + 4*a(n-4).

Conjectures from Colin Barker, Apr 10 2018: (Start)

G.f.: x*(15 - 24*x - 32*x^2 + 48*x^3) / ((1 - x)*(1 - 2*x)*(1 - 2*x^2)).

a(n) = 3*2^(n/2) + 2^(n+1) + 7 for n even.

a(n) = 2^(n+1) + 2^((n+3)/2) + 7 for n odd.

(End)

EXAMPLE

Some solutions for 5 X 3:

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

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

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

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

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

CROSSREFS

Cf. A184048.

Sequence in context: A324110 A285800 A340380 * A070005 A275384 A185307

Adjacent sequences:  A184038 A184039 A184040 * A184042 A184043 A184044

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 08 2011

STATUS

approved

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Last modified September 17 03:42 EDT 2021. Contains 347478 sequences. (Running on oeis4.)