This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A123776 #8 Jul 21 2017 13:27:05 %S A123776 5,28,185,1287,9456,71167,549076,4300975,34154107,273998400, %T A123776 2217436152,18074303774,148232462372 %N A123776 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 A123776 The base block is not counted among the n and must be the only block in the bottom layer of the building. %Y A123776 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123776 nonn,hard %O A123776 1,1 %A A123776 _Søren Eilers_, Oct 29 2006