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 A123799 #9 Nov 29 2017 03:37:32 %S A123799 1,22,43,1039,3136,81773,267670,7192059 %N A123799 Number of ways to build a contiguous building with n LEGO blocks of size 1 X 6 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees. %C A123799 The base block is not counted among the n and must be the only block in the bottom layer of the building. %Y A123799 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123799 nonn,more %O A123799 1,2 %A A123799 _Søren Eilers_, Oct 29 2006