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A198598
Number of 2n X 4 0..3 arrays with values 0..3 introduced in row major order and each element equal to exactly two horizontal and vertical neighbors.
1
1, 5, 32, 251, 1985, 15761, 125168, 994127, 7895777, 62711837, 498086240, 3956031011, 31420628321, 249557171369, 1982098563440, 15742744249463, 125036161801025, 993095073749045, 7887620760000800, 62647135102634315
OFFSET
1,2
COMMENTS
Column 2 of A198604.
LINKS
FORMULA
Empirical: a(n) = 9*a(n-1) -4*a(n-2) -36*a(n-3) +5*a(n-4) +27*a(n-5).
Empirical g.f.: x*(1 - 4*x - 9*x^2 + 19*x^3 + 29*x^4) / ((1 - x)*(1 + x)*(1 - 9*x + 5*x^2 + 27*x^3)). - Colin Barker, May 14 2018
EXAMPLE
Some solutions for n=3:
..0..0..1..1....0..0..0..0....0..0..0..0....0..0..1..1....0..0..1..1
..0..0..1..1....0..1..1..0....0..1..1..0....0..0..1..1....0..0..1..1
..1..1..0..0....0..1..1..0....0..1..1..0....2..2..2..2....2..2..3..3
..1..1..0..0....0..0..0..0....0..0..0..0....2..0..0..2....2..2..3..3
..0..0..1..1....1..1..2..2....2..2..1..1....2..0..0..2....3..3..2..2
..0..0..1..1....1..1..2..2....2..2..1..1....2..2..2..2....3..3..2..2
CROSSREFS
Cf. A198604.
Sequence in context: A127089 A241769 A208046 * A369785 A215916 A068102
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 27 2011
STATUS
approved