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A003087
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Number of acyclic digraphs with n unlabeled nodes.
(Formerly M1696)
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7
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1, 1, 2, 6, 31, 302, 5984, 243668, 20286025, 3424938010, 1165948612902, 797561675349580, 1094026876269892596, 3005847365735456265830, 16530851611091131512031070, 181908117707763484218885361402
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OFFSET
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0,3
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COMMENTS
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Also the number of equivalence classes of n X n real (0,1)-matrices with all eigenvalues positive, up to conjugation by permutations.
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REFERENCES
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F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 194.
Jack Kuipers and Giusi Moffa, Uniform generation of random acyclic digraphs, Arxiv preprint arXiv:1202.6590, 2012. - N. J. A. Sloane, Sep 14 2012
R. W. Robinson, Counting unlabeled acyclic digraphs, in "Combinatorial Mathematics V (Melbourne 1976)", Lect. Notes Math. 622 (1976), pp. 28-43.
R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1976.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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R. W. Robinson, Table of n, a(n) for n = 0..18
B. D. McKay, F. E. Oggier, G. F. Royle, N. J. A. Sloane, I. M. Wanless and H. S. Wilf, Acyclic digraphs and eigenvalues of (0,1)-matrices, J. Integer Sequences, 7 (2004), #04.3.3.
B. D. McKay, F. E. Oggier, G. F. Royle, N. J. A. Sloane, I. M. Wanless and H. S. Wilf, Acyclic digraphs and eigenvalues of (0,1)-matrices
Eric Weisstein's World of Mathematics, Acyclic Digraph.
Index entries for sequences related to binary matrices
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CROSSREFS
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Cf. A003024 (the labeled case), A082402. Rows sums of A122078.
Sequence in context: A018225 A217143 A075845 * A203901 A190958 A109243
Adjacent sequences: A003084 A003085 A003086 * A003088 A003089 A003090
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KEYWORD
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nonn,nice
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AUTHOR
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N. J. A. Sloane.
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STATUS
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approved
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