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A268635
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Number of n_X_4 0..2 arrays with some element plus some horizontally or vertically adjacent neighbor totalling two exactly once.
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1
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36, 504, 5178, 47640, 412740, 3440052, 27906474, 221913216, 1737860310, 13445785116, 103012659468, 782824552488, 5908380409134, 44334271544616, 330997648937706, 2460394469263680, 18218335277707956, 134439600276305244
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OFFSET
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1,1
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LINKS
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FORMULA
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Empirical: a(n) = 18*a(n-1) - 111*a(n-2) + 282*a(n-3) - 333*a(n-4) + 180*a(n-5) - 36*a(n-6) for n>7.
Empirical g.f.: 6*x*(6 - 24*x + 17*x^2 + 38*x^3 - 27*x^4 - 12*x^5 + 8*x^6) / (1 - 9*x + 15*x^2 - 6*x^3)^2. - Colin Barker, Jan 14 2019
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EXAMPLE
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Some solutions for n=4:
..0..0..1..0. .0..0..1..0. .2..1..2..1. .1..2..2..2. .2..1..0..1
..0..0..0..1. .2..1..0..1. .2..2..1..0. .0..2..2..1. .2..2..1..0
..1..0..1..0. .2..2..1..0. .1..1..0..0. .1..2..1..0. .1..2..1..0
..1..0..0..1. .2..1..2..1. .0..0..1..0. .2..1..2..1. .2..1..0..0
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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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