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A196630
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Number of n X 2 0..4 arrays with each element x equal to the number its horizontal and vertical neighbors equal to 1,3,2,0,4 for x=0,1,2,3,4.
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3
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1, 2, 5, 10, 26, 65, 161, 403, 1006, 2511, 6270, 15654, 39083, 97579, 243625, 608258, 1518637, 3791578, 9466426, 23634809, 59008985, 147327627, 367832622, 918367047, 2292885358, 5724642758, 14292705299, 35684571667, 89093606033, 222439846274
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OFFSET
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1,2
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COMMENTS
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Every 0 is next to 0 1's, every 1 is next to 1 3's, every 2 is next to 2 2's, every 3 is next to 3 0's, every 4 is next to 4 4's.
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LINKS
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FORMULA
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Empirical: a(n) = 2*a(n-1) + a(n-2) + a(n-3) - a(n-4).
Empirical g.f.: x*(1 - 3*x^3) / (1 - 2*x - x^2 - x^3 + x^4). - Colin Barker, Feb 22 2018
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EXAMPLE
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All solutions for n=4:
..0..0....0..0....0..0....0..0....0..0....0..0....2..2....0..0....0..0....0..0
..3..0....0..3....3..0....0..0....0..0....0..0....2..2....0..3....0..0....2..2
..0..0....0..0....0..3....3..0....2..2....0..3....0..0....3..0....0..0....2..2
..0..0....0..0....0..0....0..0....2..2....0..0....0..0....0..0....0..0....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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