

A204804


Number of free treelike convex polyominoes with n cells.


0



1, 1, 2, 4, 10, 21, 49, 104, 227, 468, 976, 1978, 4030, 8095, 16313, 32656, 65503, 130986
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OFFSET

1,3


COMMENTS

Free: none is a rigid transformation (translation, rotation, reflection or glide reflection) of another. Treelike: never does a 2x2 subarrangement of squares occur in the shape. So the dual graph is a tree. Convex: every horizontal, or vertical line, meets the shape in either a single segment, or not at all.


LINKS



EXAMPLE

n=1: one square. n=2: a 2x1 rectangle. n=3: a 3x1 rectangle; an Lshape. So the sequence starts: 1,1,2,... Images up to n=8 at the MathOverflow link.


CROSSREFS



KEYWORD

nonn,hard,more


AUTHOR



EXTENSIONS



STATUS

approved



