A001851 - OEIS

%I M1363 N0527 #28 Feb 09 2018 21:45:38

%S 0,1,2,5,9,21,44,103,232,571,1368,3441,8653,22263,57518,150733,396937,

%T 1054540,2815453,7562159,20399714,55280532,150356806,410432671,

%U 1123902587,3086827578,8500975970,23470712241,64952794778,180144093389

%N Total diameter of unlabeled trees with n nodes.

%C C program around function Gen() by Gang Li & Frank Ruskey. See C program link.

%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H W. Bomfim, <a href="http://oeis.org/wiki/File:F1.png">Diameters of the trees of order 6</a>

%H W. Bomfim, <a href="http://oeis.org/w/images/3/31/FreeTree1.txt">C program</a>

%H 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 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 <a href="/index/Tra#trees">Index entries for sequences related to trees</a>

%e See the trees in first Bomfim link. So a(6) = 21.

%K nonn

%O 1,3

%A _N. J. A. Sloane_

%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jul 26 2010

%E a(21)-a(30) from _Washington Bomfim_, Jan 31 2011