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A186161
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1/4 the number of n X 2 0..3 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, 7, 48, 321, 2175, 14748, 99933, 677283, 4590168, 31108893, 210834267, 1428886932, 9683993481, 65631317487, 444803049600, 3014563174089, 20430595384935, 138464249604684, 938413592805957, 6359909317239723
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OFFSET
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1,2
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COMMENTS
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Column 2 of A186168.
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LINKS
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R. H. Hardin, Table of n, a(n) for n = 1..200
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FORMULA
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Empirical: a(n) = 5*a(n-1) + 11*a(n-2) + 9*a(n-3) - 9*a(n-4) - 27*a(n-5).
Empirical g.f.: x*(1 + 2*x + 2*x^2 - 5*x^3 - 12*x^4) / (1 - 5*x - 11*x^2 - 9*x^3 + 9*x^4 + 27*x^5). - Colin Barker, Apr 17 2018
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EXAMPLE
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Some solutions for 4 X 2 with a(1,1)=0:
..0..0....0..1....0..0....0..0....0..3....0..2....0..0....0..2....0..2....0..0
..2..2....0..1....2..3....1..1....0..3....0..2....0..2....0..2....0..2....0..0
..0..2....3..3....2..3....3..3....2..0....0..2....3..2....3..3....1..1....2..2
..0..0....0..0....1..1....3..3....2..0....0..2....3..3....3..3....1..1....0..0
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CROSSREFS
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Cf. A186168.
Sequence in context: A227100 A240334 A171312 * A081106 A289785 A036829
Adjacent sequences: A186158 A186159 A186160 * A186162 A186163 A186164
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KEYWORD
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nonn
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AUTHOR
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R. H. Hardin, Feb 13 2011
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STATUS
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approved
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