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 A334613 #22 Oct 19 2020 13:04:11 %S A334613 1,1,1,2,7,28,151,907,6467,51151,458478,4455476,48162974,557022350, %T A334613 7020022164,94129389215,1357181821028,20661645476348 %N A334613 Number of distinct graceful labelings of bipartite graphs with n vertices and n-1 edges. %C A334613 Consider vertices numbered 1 to n. Add the edges 1--n, 2--n, and either 1--(n+1-k), 2--(n+2-k), ... or k--n for 3<=k<n. (Altogether (n-1)!/2 possibilities.) If the resulting graph has no odd cycles, this is a graceful labeling of a bipartite graph. %e A334613 For example, the seven labelings for n=5 are: %e A334613 1--5, 2--5, 1--3, 2--3; %e A334613 1--5, 2--5, 1--3, 3--4; %e A334613 1--5, 2--5, 1--3, 4--5; %e A334613 1--5, 2--5, 2--4, 2--3; %e A334613 1--5, 2--5, 2--4, 3--4; %e A334613 1--5, 2--5, 3--5, 3--4; %e A334613 1--5, 2--5, 3--5, 4--5. %e A334613 The first of these is the four-cycle plus an isolated vertex; the other six are the trees in A337274. %Y A334613 Cf. A337274. %K A334613 nonn,more %O A334613 1,4 %A A334613 _Don Knuth_, Sep 08 2020 %E A334613 a(17)-a(18) from _Bert Dobbelaere_, Sep 11 2020