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A185899
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1/8 the number of n X 2 0..7 arrays with every element equal to exactly one or two of its horizontal and vertical neighbors.
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1
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1, 15, 196, 2765, 38731, 545328, 7675381, 108065699, 1521488668, 21421955457, 301612441375, 4246586949080, 59790307544569, 841824567122343, 11852566615920436, 166879587240301061, 2349600516714827299
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 13*a(n-1) + 27*a(n-2) - 147*a(n-3) - 245*a(n-4) - 343*a(n-5).
Empirical g.f.: x*(1 + 2*x - 26*x^2 - 41*x^3 - 56*x^4) / (1 - 13*x - 27*x^2 + 147*x^3 + 245*x^4 + 343*x^5). - Colin Barker, Apr 17 2018
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EXAMPLE
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Some solutions for 3 X 2 with a(1,1)=0:
..0..1....0..0....0..6....0..0....0..0....0..0....0..0....0..0....0..0....0..7
..0..1....7..0....0..6....0..6....4..0....2..2....5..2....1..1....4..4....0..7
..1..1....7..7....5..5....6..6....4..0....3..3....5..2....3..3....1..1....7..7
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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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