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A235282 Number of (n+1) X (1+1) 0..3 arrays with every 2 X 2 subblock having its diagonal sum differing from its antidiagonal sum by 4 (constant stress 1 X 1 tilings). 1
20, 40, 68, 136, 236, 472, 836, 1672, 3020, 6040, 11108, 22216, 41516, 83032, 157316, 314632, 603020, 1206040, 2333348, 4666696, 9097196, 18194392, 35680196, 71360392, 140595020, 281190040, 556002788, 1112005576, 2204879276, 4409758552 (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) + 3*a(n-2) - 6*a(n-3).

Conjectures from Colin Barker, Oct 18 2018: (Start)

G.f.: 4*x*(5 - 18*x^2) / ((1 - 2*x)*(1 - 3*x^2)).

a(n) = 2^(2+n) + 2*3^((-1+n)/2)*(3-3*(-1)^n + 2*sqrt(3) + 2*(-1)^n*sqrt(3)).

(End)

EXAMPLE

Some solutions for n=4:

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

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

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

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

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

CROSSREFS

Column 1 of A235289.

Sequence in context: A065607 A008602 A061830 * A270296 A041790 A041788

Adjacent sequences:  A235279 A235280 A235281 * A235283 A235284 A235285

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 05 2014

STATUS

approved

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Last modified August 26 00:35 EDT 2019. Contains 326324 sequences. (Running on oeis4.)