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A123809
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 flat, i.e., with all blocks in parallel position and symmetric after a rotation by 180 degrees.
0
1, 4, 7, 34, 85, 461, 1175, 6871, 18807, 112406, 318571, 1936113, 5653062, 34848639, 103771770, 645701202, 1955873614
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
EXTENSIONS
a(11)-a(17) from Søren Eilers, Sep 16 2018
STATUS
approved