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A123823
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Number of ways to build a contiguous building with n LEGO blocks of size 2 X 2 on top of a fixed block of the same size so that the building is symmetric after a rotation by 90 degrees.
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0
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1, 1, 1, 2, 3, 4, 5, 11, 22, 34, 47, 113
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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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: A006481 A118597 A083160 * A064959 A032988 A136367
Adjacent sequences: A123820 A123821 A123822 * A123824 A123825 A123826
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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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