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A123823 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. 0
1, 1, 1, 2, 3, 4, 5, 11, 22, 34, 47, 113 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
COMMENTS
The base block is not counted among the n and must be the only block in the bottom layer of the building
LINKS
CROSSREFS
Sequence in context: A006481 A118597 A083160 * A274837 A064959 A217650
KEYWORD
nonn
AUTHOR
Søren Eilers, Oct 29 2006
STATUS
approved

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Last modified February 25 21:07 EST 2024. Contains 370333 sequences. (Running on oeis4.)