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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

%I

%S 1,5,9,44,111,576,1541,8199,23750,127654,384817,2083235

%N 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.

%C The base block is not counted among the n and must be the only block in the bottom layer of the building

%Y Cf. A112389, A123762 - A123827, A123829 - A123849.

%K nonn

%O 1,2

%A _Søren Eilers_, Oct 29 2006

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Last modified June 22 14:22 EDT 2021. Contains 345380 sequences. (Running on oeis4.)