A003244 - OEIS

%I M0759 #27 Jun 26 2017 22:39:34

%S 1,1,1,2,3,6,9,16,23,35,51,72,97,136,186,230,321,401,526,647,844,1000,

%T 1331,1539,1960,2299,2943,3307,4237,4779,5961,6744,8372,9239,11605,

%U 12694,15549,17264,21086,22784,27976,30357,36598,39843,47821

%N Number of unrooted achiral trees with n nodes.

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

%H F. Harary and R. W. Robinson, <a href="http://dx.doi.org/10.1515/crll.1975.278-279.322">The number of achiral trees</a>, J. Reine Angew. Math., 278 (1975), 322-335.

%H F. Harary and R. W. Robinson, <a href="/A002995/a002995_1.pdf">The number of achiral trees</a>, J. Reine Angew. Math., 278 (1975), 322-335. (Annotated scanned copy)

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

%F In terms of generating functions: A003244(x) = A003241(x)-(P^2(x)-P(x^2))/(2*x^2) with P(x)=x*A003238(x). [Harary & Robinson eq 45]. - _R. J. Mathar_, Sep 28 2011

%K nonn,easy

%O 1,4

%A _N. J. A. Sloane_

%E Extended by _R. J. Mathar_, Sep 28 2011