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A216581
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Number of distinct connected planar figures that can be formed from n 1x2 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.
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6
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OFFSET
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0,2
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COMMENTS
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Figures that differ by a rotation or reflection are regarded as distinct (cf. A216492).
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LINKS
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EXAMPLE
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One domino (rectangle 2x1) is placed on a table. There are two ways to do this, horizontally or vertically, so a(1)=2.
A 2nd domino is placed touching the first only in a single edge (of length 1). The number of different planar figures is a(2) = 4+8+2 = 14.
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CROSSREFS
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Without the condition that the adjacency graph forms a tree we get A216583 and A216595.
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KEYWORD
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nonn,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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