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 A123839 #6 Oct 09 2013 14:20:53 %S A123839 1,1,21,67,1565,6241,137613,630193,13136926 %N A123839 Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 4 X 4 which is symmetric after a rotation by 180 degrees. %Y A123839 Cf. A112389, A123762 - A123827, A123829 - A123849. %K A123839 nonn %O A123839 1,3 %A A123839 _Søren Eilers_, Oct 29 2006