Search: id:A001930
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%I A001930 M2817 N1133
%S A001930 1,1,3,9,33,139,718,4535,35979,363083,4717687,79501654,1744252509,
%T A001930 49872339897,1856792610995,89847422244493,5637294117525695
%N A001930 Number of topologies, or transitive digraphs with n unlabeled nodes.
%C A001930 a(13)-a(16) from Brinkmann's and McKay's paper, sent by Vladeta Jovovic 
               (vladeta(AT)eunet.rs), Jan 04 2006
%D A001930 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A001930 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A001930 Gunnar Brinkmann and Brendan D. McKay, Counting Unlabeled Topologies 
               and Transitive Relations, Journal of Integer Sequences, Vol. 8 (2005), 
               Article 05.2.1.
%D A001930 K. K.-H. Butler and G. Markowsky, Enumeration of finite topologies, Proc. 
               4th S-E Conf. Combin., Graph Theory, Computing, Congress. Numer. 
               8 (1973), 169-184.
%D A001930 F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 
               1973, p. 218 (but the last entry is wrong).
%D A001930 J. A. Wright, There are 718 6-point topologies, quasi-orderings and transgraphs, 
               Notices Amer. Math. Soc., 17 (1970), p. 646, Abstract #70T-A106.
%D A001930 J. A. Wright, personal communication.
%D A001930 For further references concerning the enumeration of topologies and posets 
               see under A000112 and A001035.
%D A001930 Moussa Benoumhani, The Number of Topologies on a Finite Set, Journal 
               of Integer Sequences, Vol. 9 (2006), Article 06.2.6.
%H A001930 Gunnar Brinkmann and Brendan D. McKay, <a href="http://cs.anu.edu.au/
               ~bdm/papers/topologies.pdf">Counting unlabeled topologies and transitive 
               relations</a>.
%H A001930 P. J. Cameron, <a href="http://www.cs.uwaterloo.ca/journals/JIS/index.html">
               Sequences realized by oligomorphic permutation groups</a>, J. Integ. 
               Seqs. Vol. 3 (2000), #00.1.5.
%H A001930 S. R. Finch, <a href="http://algo.inria.fr/bsolve/">Transitive relations, 
               topologies and partial orders</a>
%H A001930 G. Pfeiffer, <a href="http://schmidt.nuigalway.ie/~goetz/pub/posetseq.html">
               Counting Transitive Relations</a>, preprint, 2004.
%H A001930 G. Pfeiffer, <a href="http://www.cs.uwaterloo.ca/journals/JIS/">Counting 
               Transitive Relations</a>, Journal of Integer Sequences, Vol. 7 (2004), 
               Article 04.3.2.
%H A001930 D. Rusin, <a href="http://www.math.niu.edu/~rusin/known-math/97/finite.top">
               More info and references</a>
%H A001930 N. J. A. Sloane, <a href="classic.html#LOSS">Classic Sequences</a>
%H A001930 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               DigraphTopology.html">Link to a section of The World of Mathematics.</
               a>
%Y A001930 Cf. A000798 (labeled topologies), A001035 (labeled posets), A001930 (unlabeled 
               topologies), A000112 (unlabeled posets), A006057, A001928, A001929.
%Y A001930 Sequence in context: A098742 A009212 A153344 this_sequence A049425 A012584 
               A101899
%Y A001930 Adjacent sequences: A001927 A001928 A001929 this_sequence A001931 A001932 
               A001933
%K A001930 nonn,hard,nice
%O A001930 0,3
%A A001930 N. J. A. Sloane (njas(AT)research.att.com).
%E A001930 a(8)-a(12) from Goetz Pfeiffer (goetz.pfeiffer(AT)nuigalway.ie), Jan 
               21 2004

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