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A197469
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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 0,1,0,0,0 for x=0,1,2,3,4.
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1
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1, 2, 6, 12, 24, 50, 98, 194, 394, 786, 1562, 3138, 6282, 12530, 25082, 50210, 100330, 200658, 401498, 802818, 1605450, 3211442, 6422714, 12844514, 25690282, 51381138, 102759194, 205520322, 411044874, 822081650, 1644162938, 3288342434
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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 0's, every 1 is next to 1 1's, every 2 is next to 2 0's, every 3 is next to 3 0's, every 4 is next to 4 0's.
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LINKS
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FORMULA
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Empirical: a(n) = a(n-1) +4*a(n-3) for n>6.
Empirical g.f.: x*(1 + x + 4*x^2 + 2*x^3 + 4*x^4 + 2*x^5) / ((1 - 2*x)*(1 + x + 2*x^2)). - Colin Barker, May 12 2018
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EXAMPLE
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Some solutions for n=4:
..1..1....1..1....0..1....1..1....2..0....2..0....0..2....1..0....2..0....0..2
..2..0....0..2....2..1....0..2....0..3....0..2....3..0....1..2....0..3....2..0
..0..2....3..0....0..2....2..0....3..0....2..1....0..2....2..0....2..0....1..2
..1..1....0..2....2..0....1..1....0..2....0..1....1..1....0..2....1..1....1..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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