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A123769
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Number of ways to build a contiguous building with n LEGO blocks of size 1x2 on top of a fixed block of the same size so that the builing is flat, i.e. with all blocks in parallel position and symmetric after a rotation by 180 degrees.
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0
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1, 2, 3, 6, 11, 23, 43, 93, 181, 392, 783, 1710, 3467, 7623, 15655, 34543, 71688, 158721, 332006, 737213
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| The base block is not counted among the n and must be the only block in the bottom layer of the building
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REFERENCES
| M. Abrahamsen and S. Eilers, Efficient counting of LEGO buildings, in preparation
B. Durhuus and S. Eilers, On the entropy of LEGO, arXiv:math.CO/0504039
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LINKS
| S. Eilers, LEGO counts
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CROSSREFS
| Sequence in context: A007477 A096202 A036653 * A093304 A036590 A036591
Adjacent sequences: A123766 A123767 A123768 * A123770 A123771 A123772
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KEYWORD
| nonn
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AUTHOR
| Soren Eilers (eilers(AT)math.ku.dk), Oct 29 2006
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