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 A123821 #6 Oct 09 2013 14:20:53 %S A123821 9,97,1349,20288,329707,5574248,97506021,1747201171,31923371982, %T A123821 592403479154 %N A123821 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. %C A123821 The base block is not counted among the n and must be the only block in the bottom layer of the building %Y A123821 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123821 nonn,hard %O A123821 1,1 %A A123821 _Søren Eilers_, Oct 29 2006