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 A123823 #8 Feb 15 2025 15:41:45 %S A123823 1,1,1,2,3,4,5,11,22,34,47,113 %N A123823 Number of ways to build a contiguous building with n LEGO blocks of size 2 X 2 on top of a fixed block of the same size so that the building is symmetric after a rotation by 90 degrees. %C A123823 The base block is not counted among the n and must be the only block in the bottom layer of the building. %Y A123823 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123823 nonn %O A123823 1,4 %A A123823 _Søren Eilers_, Oct 29 2006