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 A129399 #2 May 20 2014 14:52:32 %S A129399 1,9,-11,33 %N A129399 Level sums of A129398. %e A129399 a(2)=-11 because it is the sum of all elements for h=2 in A129398: %e A129399 .....1 %e A129399 ..1.-3..1 %e A129399 1.-3.-7.-3..1 %e A129399 ..1..3..1 %e A129399 .....1 %Y A129399 Cf. A129398. %K A129399 sign %O A129399 0,2 %A A129399 _Jonas Wallgren_, Apr 13 2007