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 A265500 #9 Jan 09 2016 14:58:19 %S A265500 1,2,7,21,52,167,501,1503,4509,13527,40581 %N A265500 Balance scale sequence. %C A265500 Every natural number up to sum(a[1], a[i]) can be written as adding or subtracting unique entries up to a(i). %H A265500 The Ben Paul Thurston Blog, <a href="http://benpaulthurstonblog.blogspot.com/2015/12/combination-series.html">Balance scale series</a> %F A265500 a(i+1)= 1+2*sum(a[1], a[i]) (proved). %e A265500 17 = 21-7+1+2, 18=21-1-2, 19=17+2. %K A265500 nonn,more %O A265500 1,2 %A A265500 _Ben Paul Thurston_, Dec 09 2015