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A209505
Half the number of (n+1) X 3 0..2 arrays with every 2 X 2 subblock having two or four distinct clockwise edge differences.
1
27, 123, 561, 2559, 11673, 53247, 242889, 1107951, 5053977, 23053983, 105161961, 479701839, 2188185273, 9981522687, 45531242889, 207693169071, 947403359577, 4321630459743, 19713345579561, 89923466978319, 410190643732473
OFFSET
1,1
COMMENTS
Column 2 of A209511.
LINKS
FORMULA
Empirical: a(n) = 5*a(n-1) -2*a(n-2).
Empirical g.f.: 3*x*(9 - 4*x) / (1 - 5*x + 2*x^2). - Colin Barker, Jul 10 2018
EXAMPLE
Some solutions for n=4:
..2..0..1....2..1..2....2..0..1....2..0..1....2..1..0....0..2..1....1..2..1
..0..1..0....0..2..1....0..2..0....0..1..2....0..2..1....1..0..2....0..1..2
..2..0..1....1..0..2....1..0..1....2..0..1....1..0..2....2..1..0....1..2..1
..0..1..2....0..1..0....2..1..0....1..2..0....2..1..0....1..2..1....0..1..2
..1..2..0....2..0..1....1..0..2....2..1..2....0..2..1....2..0..2....1..0..1
CROSSREFS
Cf. A209511.
Sequence in context: A087795 A036927 A232025 * A275430 A145555 A293894
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 09 2012
STATUS
approved