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A221652
Number of n X 2 arrays of occupancy after each element moves to some horizontal, diagonal or antidiagonal neighbor, without move-in move-out left turns.
2
1, 4, 12, 40, 136, 460, 1556, 5264, 17808, 60244, 203804, 689464, 2332440, 7890588, 26693668, 90304032, 305496352, 1033486756, 3496260652, 11827765064, 40013042600, 135363153516, 457930268212, 1549167000752, 5240794423984
OFFSET
1,2
COMMENTS
Column 2 of A221655.
LINKS
FORMULA
Empirical: a(n) = 3*a(n-1) + a(n-2) + a(n-3) for n>4.
Empirical g.f.: x*(1 - x)*(1 + x)^2 / (1 - 3*x - x^2 - x^3). - Colin Barker, Mar 14 2018
EXAMPLE
Some solutions for n=3:
..0..2....0..1....1..1....2..1....1..1....0..1....0..1....1..1....0..2....1..1
..2..1....2..1....1..1....0..0....0..2....2..2....1..2....1..2....2..0....0..1
..1..0....1..1....1..1....1..2....2..0....1..0....2..0....1..0....1..1....2..1
CROSSREFS
Cf. A221655.
Sequence in context: A289653 A081875 A102433 * A259806 A100320 A064649
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 21 2013
STATUS
approved