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A183624
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Number of (n+1) X 2 0..2 arrays with every 2 x 2 subblock summing to 4.
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3
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19, 45, 115, 309, 859, 2445, 7075, 20709, 61099, 181245, 539635, 1610709, 4815739, 14414445, 43177795, 129402309, 387944779, 1163310045, 3488881555, 10464547509, 31389448219, 94159956045, 282463090915, 847355718309, 2542000046059
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OFFSET
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1,1
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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) - 11*a(n-2) + 6*a(n-3).
G.f.: x*(19 - 69*x + 54*x^2) / ((1 - x)*(1 - 2*x)*(1 - 3*x)).
a(n) = 2 + 2^(2+n) + 3^(1+n).
(End)
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EXAMPLE
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Some solutions for 3 X 2:
..2..0....2..0....1..2....2..0....1..0....0..2....2..1....0..2....2..0....0..2
..2..0....1..1....1..0....0..2....1..2....0..2....0..1....1..1....2..0....2..0
..2..0....2..0....2..1....1..1....0..1....1..1....1..2....1..1....1..1....0..2
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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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