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A198474
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Number of 2n X 2 0..2 arrays with values 0..2 introduced in row major order and each element equal to an odd number of horizontal and vertical neighbors.
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2
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2, 12, 76, 492, 3212, 21036, 137932, 904812, 5936396, 38950572, 255572812, 1676946156, 11003350412, 72199015212, 473737530316, 3108453529452, 20396281280012, 133831275048876, 878140974959692, 5761968373855212
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 9*a(n-1) - 16*a(n-2).
G.f.: 2*x*(1 - 3*x) / (1 - 9*x + 16*x^2).
a(n) = (2^(-4-n)*((9-sqrt(17))^n*(-5+3*sqrt(17)) + (9+sqrt(17))^n*(5+3*sqrt(17)))) / sqrt(17).
(End)
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EXAMPLE
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Some solutions for n=3:
..0..1....0..0....0..0....0..0....0..1....0..1....0..0....0..1....0..0....0..0
..0..1....1..1....1..1....1..1....0..1....0..1....1..2....0..1....1..1....1..1
..2..2....2..2....0..0....0..0....2..2....2..0....1..2....1..2....2..0....2..2
..1..1....1..1....1..1....2..2....0..0....2..0....0..0....1..2....2..0....0..0
..0..0....2..2....2..2....1..0....1..2....1..1....1..1....0..0....0..2....2..2
..1..1....1..1....0..0....1..0....1..2....2..2....2..2....1..1....0..2....1..1
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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