

A003087


Number of acyclic digraphs with n unlabeled nodes.
(Formerly M1696)


21



1, 1, 2, 6, 31, 302, 5984, 243668, 20286025, 3424938010, 1165948612902, 797561675349580, 1094026876269892596, 3005847365735456265830, 16530851611091131512031070, 181908117707763484218885361402
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OFFSET

0,3


COMMENTS

Also the number of equivalence classes of n X n real (0,1)matrices with all eigenvalues positive, up to conjugation by permutations.


REFERENCES

F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 194.
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).


LINKS

R. W. Robinson, Counting unlabeled acyclic digraphs, in Little C.H.C. (Ed.), "Combinatorial Mathematics V (Melbourne 1976)", Lect. Notes Math. 622 (1976), pp. 2843. DOI:10.1007/BFb0069178.


CROSSREFS



KEYWORD

nonn,nice


AUTHOR



STATUS

approved



