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 A123820 #6 Oct 09 2013 14:20:53 %S A123820 1,1,1,1,3,4,5,10,26,38,51,121,324,488,673,1808 %N A123820 Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 2 X 2 which is symmetric after a rotation by 90 degrees. %Y A123820 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123820 nonn %O A123820 1,5 %A A123820 _Søren Eilers_, Oct 29 2006