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Search: id:A003087
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| A003087 |
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Number of acyclic digraphs with n unlabeled nodes.
(Formerly M1696)
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+0
6
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| 1, 1, 2, 6, 31, 302, 5984, 243668, 20286025, 3424938010, 1165948612902, 797561675349580, 1094026876269892596, 3005847365735456265830, 16530851611091131512031070, 181908117707763484218885361402
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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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.
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.
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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, Link to a section of The World of Mathematics.
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: A113719 A018225 A075845 this_sequence A109243 A108327 A121071
Adjacent sequences: A003084 A003085 A003086 this_sequence A003088 A003089 A003090
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KEYWORD
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nonn,nice
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AUTHOR
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njas
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