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 A006680 M4427 #20 Jul 08 2025 16:52:29 %S A006680 1,1,7,45,465,5775,88515,1588545,32852925,768242475,20053670175, %T A006680 577971719325,18230691904425,624676513836375,23106221910646875, %U A006680 917643290676737625,38944796393877499125,1759004961887566267875 %N A006680 Number of binary phylogenetic trees with n labels. %D A006680 Foulds, L. R.; Robinson, R. W. Enumeration of binary phylogenetic trees. Combinatorial mathematics, VIII (Geelong, 1980), pp. 187-202, Lecture Notes in Math., 884, Springer, Berlin-New York, 1981. Math. Rev. 83a:05071. %D A006680 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A006680 L. R. Foulds and R. W. Robinson, <a href="/A006677/a006677.pdf">Enumeration of binary phylogenetic trees</a>, pp. 187-202, Lecture Notes in Math., 884, Springer, Berlin-New York, 1981. (Annotated scanned copy) %H A006680 <a href="/index/Tra#trees">Index entries for sequences related to trees</a> %F A006680 a(2) = 1, a(n) = A006678(n-1) + 2*(n-1)*A006678(n-2) - (n+1)*a(n-1) for n >= 3. - _Sean A. Irvine_, Jun 16 2017 %K A006680 nonn %O A006680 2,3 %A A006680 _N. J. A. Sloane_ %E A006680 More terms and offset corrected by _Sean A. Irvine_, Jun 16 2017