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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
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OFFSET
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1,4
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COMMENTS
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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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LINKS
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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