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 A123827 #11 Nov 29 2017 03:38:18 %S A123827 1,13,25,352,1006,15510,46928,744211,2479362 %N A123827 Number of ways to build a contiguous building with n LEGO blocks of size 2 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 A123827 The base block is not counted among the n and must be the only block in the bottom layer of the building. %H A123827 <a href="/wiki/Index_to_OEIS:_Section_Lc#LEGO">Index entry for sequences related to LEGO blocks</a> %Y A123827 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123827 nonn,more %O A123827 1,2 %A A123827 _Søren Eilers_, Oct 29 2006