A182948 Number of complete sphere stacks on a rhombic base with side lengths n.

1, 2, 9, 154, 11358, 3235665

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

Table of n, a(n) for n=1..6.

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

Adjacent sequences: A182945 A182946 A182947 * A182949 A182950 A182951

Keyword

nonn,more

Author

David Scambler, Dec 14 2010

Status

approved