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 A058866 #11 Sep 02 2022 19:17:46 %S A058866 1,2,6,21,83,356,1599,7434,35381,171508,843419,4197179,21094355, %T A058866 106915928,545859112,2804656069,14491370996,75248398034,392476363133, %U A058866 2055245992376,10801442696736,56953957110855,301207378815752 %N A058866 Number of 2-trees rooted at an edge. %D A058866 F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 75, Eq. (3.5.11). %F A058866 H. and P. give g.f. %Y A058866 Let A063687(n) be the number of 2-trees rooted at a symmetric edge (see H. and P. Eq. (3.5.9)). Then A058866(n) = A058870(n) + A063687(n). %Y A058866 Cf. A058870, A054581. %K A058866 nonn,easy %O A058866 1,2 %A A058866 _N. J. A. Sloane_, Jan 06 2001 %E A058866 More terms from _Vladeta Jovovic_, Aug 22 2001