

A006608


Number of nnode graphs not determined by their spectrum.
(Formerly M1981)


1



0, 0, 0, 0, 2, 10, 110, 1722, 51039, 2560606, 215331676, 31067572481
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OFFSET

1,5


REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Table of n, a(n) for n=1..12.
Andries E. Brouwer, Numbers of characteristic polynomials and cospectral graphs for A
A. E. Brouwer and E. Spence, Cospectral graphs on 12 vertices, Electr. J. Combin. 16 (2009) N20. (p. 199).
C. Godsil and B. D. McKay, Some computational results on the spectra of graphs, pp. 7392 of Combinatorial Mathematics IV (Adelaide 1975), Lect. Notes Math., 560 (1976).
E. Spence, Numbers of characteristic polynomials and cospectral graphs for A
Eric Weisstein's World of Mathematics, Determined by Spectrum


CROSSREFS

Cf. A178925 (simple graphs determined by spectrum).
Sequence in context: A240625 A062412 A212491 * A066205 A113147 A335946
Adjacent sequences: A006605 A006606 A006607 * A006609 A006610 A006611


KEYWORD

nonn,hard,more


AUTHOR

N. J. A. Sloane.


EXTENSIONS

a(10) from Eric W. Weisstein, Dec 30 2010
Two more terms from Ruperto Corso, Dec 18 2011


STATUS

approved



