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 A058668 #5 Mar 30 2012 16:48:56 %S A058668 0,1,2,5,6,13,28 %N A058668 Number of unlabeled graphs with n edges, no nodes of degree 1 and no cut nodes, under "series-equivalence"; multiple edges are allowed. %C A058668 Under "series-equivalence" two graphs are equivalent if one can be obtained from the other by exchanging two subgraphs in series: replacing -A-B- by -B-A-. %C A058668 Start with the graph consisting of a single edge together with the graphs described in A058642; apply the operations of replacing edges by two edges in series or parallel; discard equivalent graphs; the result is A058668. %D A058668 B. D. H. Tellegen, Geometrical configurations and duality of electrical networks, Philips Technical Review, 5 (1940), 324-330. %Y A058668 Cf. A058642. %K A058668 nonn,nice,more %O A058668 1,3 %A A058668 _N. J. A. Sloane_, Dec 30 2000