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A123822
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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 180 degrees.
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0
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1, 5, 9, 44, 111, 576, 1541, 8199, 23750, 127654, 384817, 2083235
(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: A176967 A110421 A176751 * A145031 A121724 A149496
Adjacent sequences: A123819 A123820 A123821 * A123823 A123824 A123825
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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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