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A123807
Number of ways to build a contiguous building with n LEGO blocks of size 1 X 7 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees.
0
2, 28, 104, 1783, 9593, 187265, 1093734
OFFSET
1,1
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,more
AUTHOR
Søren Eilers, Oct 29 2006
STATUS
approved