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A182947
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Complete sphere stacks on a triangular base
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1
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OFFSET
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1,3
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COMMENTS
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Start with a layer of spheres closely packed in an equilateral triangle of side n >= 1. Add spheres by resting them in any of the hollows between three touching spheres in the layer below. Continue until no more sites are available.
a(n) is the number of distinct complete stacks that can be built.
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LINKS
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Table of n, a(n) for n=1..8.
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EXAMPLE
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For n=3 there are two complete stacks, so a(3)=2.
3 layers, 10 spheres 2 layers, 7 spheres
1 1
. . . .
. 2 . . . .
1 . . 1 1 . . 1
. . 3 . . . . 2 . .
. 2 . . 2 . . . . . . .
1 . . 1 . . 1 1 . . 1 . . 1
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CROSSREFS
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Cf. A182948 = spheres on a rhombic base
Sequence in context: A058164 A006059 A277406 * A006041 A192551 A121131
Adjacent sequences: A182944 A182945 A182946 * A182948 A182949 A182950
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KEYWORD
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nonn
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AUTHOR
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David Scambler, Dec 14 2010
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STATUS
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approved
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