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 A123784 #8 Jul 21 2017 13:27:10 %S A123784 7,55,511,5000,51674,547204,5940045,65472189,731569499,8258444996, %T A123784 94045306573 %N A123784 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. %C A123784 The base block is not counted among the n and must be the only block in the bottom layer of the building. %Y A123784 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123784 nonn,hard %O A123784 1,1 %A A123784 _Søren Eilers_, Oct 29 2006