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A209506
Half the number of (n+1) X 4 0..2 arrays with every 2 X 2 subblock having two or four distinct clockwise edge differences.
1
81, 561, 3906, 27225, 189801, 1323270, 9225765, 64321641, 448447914, 3126561201, 21798261945, 151976626974, 1059575080797, 7387315894233, 51504076597986, 359084401453161, 2503522359474057, 17454459673057014, 121691808074121237
OFFSET
1,1
COMMENTS
Column 3 of A209511.
LINKS
FORMULA
Empirical: a(n) = 9*a(n-1) - 15*a(n-2) + 6*a(n-3).
Empirical g.f.: 3*x*(27 - 56*x + 24*x^2) / (1 - 9*x + 15*x^2 - 6*x^3). - Colin Barker, Jul 10 2018
EXAMPLE
Some solutions for n=4:
..0..1..0..2....2..0..1..2....1..2..0..1....2..1..2..1....0..1..2..1
..1..0..1..0....1..2..0..1....2..0..1..0....1..2..0..2....2..0..1..2
..2..1..0..1....2..1..2..0....1..2..0..1....2..0..2..1....0..1..2..1
..0..2..1..2....0..2..1..2....2..1..2..0....1..2..0..2....2..0..1..2
..1..0..2..1....1..0..2..1....0..2..0..2....2..0..1..0....0..1..0..1
CROSSREFS
Cf. A209511.
Sequence in context: A186141 A185771 A186133 * A139156 A237035 A237028
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 09 2012
STATUS
approved