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A204804
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Number of free tree-like convex polyominoes with n cells.
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0
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1, 1, 2, 4, 10, 21, 49, 104, 227, 468, 976, 1978, 4030, 8095, 16313, 32656, 65503, 130986
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listen;
history;
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internal format)
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OFFSET
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1,3
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COMMENTS
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Free: none is a rigid transformation (translation, rotation, reflection or glide reflection) of another. Tree-like: 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.
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LINKS
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EXAMPLE
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n=1: one square. n=2: a 2x1 rectangle. n=3: a 3x1 rectangle; an L-shape. So the sequence starts: 1,1,2,... Images up to n=8 at the MathOverflow link.
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CROSSREFS
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KEYWORD
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nonn,hard,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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