

A123785


Number of ways to build a contiguous building with n LEGO blocks of size 1 X 4 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, 3, 5, 16, 36, 124, 287, 1043, 2573, 9448, 24161, 89827, 235902, 886047, 2372494, 8968829, 24410414, 92783928, 255723571, 976331352
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