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A123822
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.
0
1, 5, 9, 44, 111, 576, 1541, 8199, 23750, 127654, 384817, 2083235
OFFSET
1,2
COMMENTS
The base block is not counted among the n and must be the only block in the bottom layer of the building
CROSSREFS
KEYWORD
nonn
AUTHOR
Søren Eilers, Oct 29 2006
STATUS
approved