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A123791
Number of ways to build a contiguous building with n LEGO blocks of size 1 X 5 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees.
0
2, 16, 56, 552, 2722, 30836, 164018, 1941658
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