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A182948 Number of complete sphere stacks on a rhombic base with side lengths n. 1
1, 2, 9, 154, 11358, 3235665 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Start with a layer of spheres closely packed in a rhombus (diamond) 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.
LINKS
EXAMPLE
For n=2 there are two complete stacks so a(2)=2.
.
1-----------1 1-----------1
\ / \ \ / \
\ 2 / \ \ / \
\ / \ or \ / \
\ / \ \ / 2 \
\ / \ \ / \
1-----------1 1-----------1
CROSSREFS
Cf. A182947 = spheres on a triangular base.
Sequence in context: A117116 A211935 A133468 * A081459 A336213 A038843
KEYWORD
nonn,more
AUTHOR
David Scambler, Dec 14 2010
STATUS
approved

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Last modified April 22 21:06 EDT 2024. Contains 371906 sequences. (Running on oeis4.)