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Search: id:A001174
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| A001174 |
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Number of oriented graphs (i.e. digraphs with no bidirected edges) on n unlabeled nodes. Also number of complete digraphs on n unlabeled nodes. Number of antisymmetric relations (i.e. oriented graphs with loops) on n unlabeled nodes is A083670.
(Formerly M1809 N0715)
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+0
12
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| 1, 2, 7, 42, 582, 21480, 2142288, 575016219, 415939243032, 816007449011040, 4374406209970747314, 64539836938720749739356, 2637796735571225009053373136, 300365896158980530053498490893399
(list; graph; listen)
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OFFSET
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1,2
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REFERENCES
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R. L. Davis, The number of structures of finite relations, Proc. Amer. Math. Soc. 4 (1953), 486-495.
F. Harary and E. M. Palmer, Enumeration of mixed graphs, Proc. Amer. Math. Soc., 17 (1966), 682-687.
F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 133, c_p.
M. D. McIlroy, Calculation of numbers of structures of relations on finite sets, Massachusetts Institute of Technology, Research Laboratory of Electronics, Quarterly Progress Reports, No. 17, Sept. 15, 1955, pp. 14-22.
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LINKS
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P. J. Cameron, Sequences realized by oligomorphic permutation groups, J. Integ. Seqs. Vol. 3 (2000), #00.1.5.
G. Pfeiffer, Counting Transitive Relations, Journal of Integer Sequences, Vol. 7 (2004), Article 04.3.2.
Eric Weisstein's World of Mathematics, Oriented Graph
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FORMULA
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There's an explicit formula - see for example Harary and Palmer (book), Eq. (5.4.14).
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CROSSREFS
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Cf. A000595, A001173.
Cf. A047656 (labeled case), A054941 (connected labeled case), A086345 (connected unlabeled case).
Adjacent sequences: A001171 A001172 A001173 this_sequence A001175 A001176 A001177
Sequence in context: A005130 A091669 A108042 this_sequence A067975 A065298 A091877
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KEYWORD
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nonn,nice,easy
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AUTHOR
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njas
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EXTENSIONS
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More terms from Vladeta Jovovic (vladeta(AT)Eunet.yu)
Revised description from Vladeta Jovovic (vladeta(AT)Eunet.yu), Jan 20 2005
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