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 A171579 #4 Jan 14 2013 04:55:10 %S A171579 0,1,1,2,5,12,27,70,192,589,1825,5870,18952,62997,211014,718474, %T A171579 2468741,8578400 %N A171579 Number of fixed polyominoes in equilibrium; a fixed polyomino is in equilibrium when its center of mass is vertically aligned with a cell with minimal coordinate. %e A171579 For n=3, we have 2 fixed polyominoes in equilibrium: namely the vertical 3-omino and the horizontal 3-omino, thus a(3)=2. %Y A171579 Cf. A001168 %K A171579 hard,more,nonn %O A171579 1,4 %A A171579 Mark Elduck (mark.elduck(AT)gmail.com), Dec 12 2009, Dec 20 2009, Dec 21 2009