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A183336
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Number of n X 4 binary arrays with each 1 adjacent to exactly one 1 vertically and one 1 horizontally.
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1
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1, 4, 7, 12, 26, 51, 97, 193, 380, 741, 1456, 2860, 5605, 10997, 21581, 42332, 83047, 162936, 319650, 627099, 1230289, 2413641, 4735192, 9289761, 18225136, 35754992, 70146009, 137616081, 269982313, 529665276, 1039124759, 2038608652, 3999447882
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OFFSET
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1,2
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COMMENTS
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Equivalent to all 1s connected only in 2 X 2 blocks.
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LINKS
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FORMULA
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Empirical: a(n) = a(n-1) + a(n-2) + 2*a(n-3) - a(n-5).
Empirical g.f.: x*(1 + x)^2*(1 + x - x^2) / (1 - x - x^2 - 2*x^3 + x^5). - Colin Barker, Mar 27 2018
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EXAMPLE
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Some solutions for 5 X 4:
..0..0..0..0....0..0..0..0....1..1..0..0....0..0..0..0....0..1..1..0
..0..0..0..0....0..0..0..0....1..1..0..0....0..1..1..0....0..1..1..0
..0..0..1..1....0..0..0..0....0..0..0..0....0..1..1..0....0..0..0..0
..0..0..1..1....0..0..1..1....0..1..1..0....0..0..0..0....1..1..0..0
..0..0..0..0....0..0..1..1....0..1..1..0....0..0..0..0....1..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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