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 A123775 #8 Oct 11 2022 22:57:53 %S A123775 2,8,24,115,451,2474,10377,60048,268402,1600292,7416480 %N A123775 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 symmetric after a rotation by 180 degrees. %C A123775 The base block is not counted among the n and must be the only block in the bottom layer of the building. %Y A123775 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123775 nonn %O A123775 1,1 %A A123775 _Søren Eilers_, Oct 29 2006