%I #8 Jul 21 2017 13:27:05
%S 5,28,185,1287,9456,71167,549076,4300975,34154107,273998400,
%T 2217436152,18074303774,148232462372
%N Number of ways to build a contiguous building with n LEGO blocks of size 1 X 3 on top of a fixed block of the same size so that the building is flat, i.e., with all blocks in parallel position.
%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,hard
%O 1,1
%A _Søren Eilers_, Oct 29 2006