OFFSET
0,3
COMMENTS
Figures that differ only by a rotation and/or reflection are regarded as equivalent (cf. A216581).
LINKS
N. J. A. Sloane, Illustration of initial terms of A056786, A216598, A216583, A216595, A216492, A216581 (Exclude figures marked (A) or (B))
N. J. A. Sloane, Illustration of third term of A056786, A216598, A216583, A216595, A216492, A216581 (a better drawing for the third term)
M. Vicher, Polyforms
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
KEYWORD
nonn,more,nice
AUTHOR
César Eliud Lozada, Sep 07 2012
EXTENSIONS
Edited by N. J. A. Sloane, Sep 09 2012
STATUS
approved