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 A001851 M1363 N0527 #28 Feb 09 2018 21:45:38 %S A001851 0,1,2,5,9,21,44,103,232,571,1368,3441,8653,22263,57518,150733,396937, %T A001851 1054540,2815453,7562159,20399714,55280532,150356806,410432671, %U A001851 1123902587,3086827578,8500975970,23470712241,64952794778,180144093389 %N A001851 Total diameter of unlabeled trees with n nodes. %C A001851 C program around function Gen() by Gang Li & Frank Ruskey. See C program link. %D A001851 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). %D A001851 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A001851 W. Bomfim, <a href="http://oeis.org/wiki/File:F1.png">Diameters of the trees of order 6</a> %H A001851 W. Bomfim, <a href="http://oeis.org/w/images/3/31/FreeTree1.txt">C program</a> %H A001851 J. Riordan, <a href="http://dx.doi.org/10.1147/rd.45.0473">Enumeration of trees by height and diameter</a>, IBM J. Res. Dev. 4 (1960), 473-478. %H A001851 J. Riordan, <a href="/A007401/a007401_8.pdf">The enumeration of trees by height and diameter</a>, IBM Journal 4 (1960), 473-478. (Annotated scanned copy) %H A001851 <a href="/index/Tra#trees">Index entries for sequences related to trees</a> %e A001851 See the trees in first Bomfim link. So a(6) = 21. %K A001851 nonn %O A001851 1,3 %A A001851 _N. J. A. Sloane_ %E A001851 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jul 26 2010 %E A001851 a(21)-a(30) from _Washington Bomfim_, Jan 31 2011