%I A002861 M1182 N0455
%S A002861 1,2,4,9,20,51,125,329,862,2311,6217,16949,46350,127714,
%T A002861 353272,981753,2737539,7659789,21492286,60466130,170510030,
%U A002861 481867683,1364424829,3870373826,10996890237,31293083540
%N A002861 Number of connected functions (or mapping patterns) on n unlabeled points, 
               or number of rings and branches with n edges.
%D A002861 S. R. Finch, Mathematical Constants, Cambridge, 2003, Section 5.6.6.
%D A002861 R. A. Fisher, Contributions to Mathematical Statistics, Wiley, 1950, 
               41.399.
%D A002861 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A002861 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A002861 C. G. Bower, <a href="b002861.txt">Table of n, a(n) for n = 1..500</a>
%H A002861 C. G. Bower, <a href="transforms2.html">Transforms (2)</a>
%H A002861 INRIA Algorithms Project, <a href="http://algo.inria.fr/bin/encyclopedia?Search=ECSnb&argsearch=118">
               Encyclopedia of Combinatorial Structures 118</a>
%F A002861 CIK transform of A000081.
%p A002861 spec2861 := [B, {A=Prod(Z,Set(A)), B=Cycle(A)}, unlabeled]; [seq(combstruct[count](spec2861,
               size=n), n=1..27)];
%Y A002861 Cf. A000081, A001372.
%Y A002861 Sequence in context: A128496 A134955 A027881 this_sequence A032200 A130969 
               A034750
%Y A002861 Adjacent sequences: A002858 A002859 A002860 this_sequence A002862 A002863 
               A002864
%K A002861 nonn,nice
%O A002861 1,2
%A A002861 N. J. A. Sloane (njas(AT)research.att.com).
%E A002861 More terms from Philippe Flajolet and Paul Zimmermann, Mar 15 1996.