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A203454
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Number of n X 2 0..2 arrays with every nonzero element less than or equal to at least two horizontal and vertical neighbors.
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1
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1, 3, 9, 22, 63, 209, 686, 2228, 7365, 24619, 82433, 276500, 929936, 3133114, 10566260, 35661359, 120433051, 406897030, 1375168827, 4648638160, 15716950105, 53145110566, 179719928744, 607794550141, 2055594816788, 6952369432018
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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) = 6*a(n-1) -12*a(n-2) +19*a(n-3) -32*a(n-4) +15*a(n-5) -13*a(n-6) +13*a(n-7) +10*a(n-8) +7*a(n-9) +5*a(n-10) +a(n-11).
Empirical g.f.: x*(1 - 3*x + 3*x^2 - 15*x^3 + 14*x^4 + 5*x^5 + 26*x^6 + 18*x^7 + 12*x^8 + 6*x^9 + x^10) / (1 - 6*x + 12*x^2 - 19*x^3 + 32*x^4 - 15*x^5 + 13*x^6 - 13*x^7 - 10*x^8 - 7*x^9 - 5*x^10 - x^11). - Colin Barker, Jun 04 2018
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EXAMPLE
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Some solutions for n=5:
..0..0....1..1....2..2....1..1....2..2....2..2....1..1....0..0....0..0....1..1
..0..0....1..1....2..2....2..2....2..2....2..2....1..1....0..0....2..2....1..1
..1..1....0..0....0..0....2..2....0..2....2..2....2..2....1..1....2..2....2..2
..2..2....2..2....0..0....0..0....2..2....1..1....2..2....1..1....0..0....2..2
..2..2....2..2....0..0....0..0....2..2....0..0....1..1....0..0....0..0....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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