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 A063687 #4 May 10 2013 12:44:50 %S A063687 1,1,1,2,3,6,10,21,38,84,156,352,677,1562,3054,7148,14196,33603,67474, %T A063687 161121,326519,785305,1603111,3878194,7965845,19365811,39983300, %U A063687 97610247,202424674,495955345,1032460679,2537529717,5300256499 %N A063687 Number of 2-trees rooted at any symmetric edge. %D A063687 F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 75, Eq. (3.5.9). %Y A063687 Cf. A058870, A058866, A054581. %K A063687 nonn %O A063687 0,4 %A A063687 _Vladeta Jovovic_, Aug 22 2001