|
|
A216492
|
|
Number of inequivalent connected planar figures that can be formed from n 1 X 2 rectangles (or dominoes) such that each pair of touching rectangles shares exactly one edge, of length 1, and the adjacency graph of the rectangles is a tree.
|
|
8
|
|
|
|
OFFSET
|
0,3
|
|
COMMENTS
|
Figures that differ only by a rotation and/or reflection are regarded as equivalent (cf. A216581).
A216583 is A216492 without the condition that the adjacency graph of the dominoes forms a tree.
|
|
LINKS
|
|
|
EXAMPLE
|
One domino (2 X 1 rectangle) is placed on a table.
A 2nd domino is placed touching the first only in a single edge (length 1). The number of different planar figures is a(2)=3.
A 3rd domino is placed in any of the last figures, touching it and sharing just a single edge with it. The number of different planar figures is a(3)=18.
When n=4, we might place 4 dominoes in a ring, with a free square in the center. This is however not allowed, since the adjacency graph is a cycle, not a tree.
|
|
CROSSREFS
|
Without the condition that the adjacency graph forms a tree we get A216583 and A216595.
|
|
KEYWORD
|
nonn,more,nice
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|