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 A243013 #6 May 31 2014 21:30:19 %S A243013 1,1,1,3,5,12,36 %N A243013 Number of graphs with n vertices and n-1 edges that can be gracefully labeled. %C A243013 Hand calculated by grade 3 students up to term 6: (1,1,1,3,5,12...) %e A243013 a(5) = 5: A001433 tells us that there are 6 simple graphs with 5 vertices and 4 edges. Only 5 of these can be labeled gracefully. The one that cannot is the triangular loop plus two connected nodes: ∆ / . %Y A243013 A001433 provides an upper bound. If the Graceful Tree Conjecture were true, A000055 would be a lower bound. %K A243013 more,nonn %O A243013 1,4 %A A243013 _Gordon Hamilton_, May 28 2014