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 A123822 #6 Oct 09 2013 14:20:53 %S A123822 1,5,9,44,111,576,1541,8199,23750,127654,384817,2083235 %N A123822 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 180 degrees. %C A123822 The base block is not counted among the n and must be the only block in the bottom layer of the building %Y A123822 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123822 nonn %O A123822 1,2 %A A123822 _Søren Eilers_, Oct 29 2006