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A218657
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Hilltop maps: number of n X 2 binary arrays indicating the locations of corresponding elements not exceeded by any king-move neighbor in a random 0..1 n X 2 array.
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2
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3, 15, 57, 225, 891, 3519, 13905, 54945, 217107, 857871, 3389769, 13394241, 52925643, 209128959, 826346529, 3265203393, 12902036643, 50980759695, 201443999193, 795980386593, 3145215436443, 12427919466687, 49107345869169
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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) = 3*a(n-1) + 3*a(n-2) + 3*a(n-3).
Empirical g.f.: 3*x*(1 + x)^2 / (1 - 3*x - 3*x^2 - 3*x^3). - Colin Barker, Mar 10 2018
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EXAMPLE
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Some solutions for n=3:
..1..1....1..1....1..0....0..0....1..1....0..1....0..1....0..0....1..1....0..0
..1..1....1..0....1..1....0..1....0..1....0..0....1..0....1..0....0..1....0..1
..1..1....0..1....1..1....0..0....0..1....1..0....0..1....1..1....0..0....0..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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