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A006608
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Number of n-node graphs not determined by their spectrum.
(Formerly M1981)
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1
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0, 0, 0, 0, 2, 10, 110, 1722, 51039, 2560606, 215331676, 31067572481
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,5
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REFERENCES
| C. Godsil and B. D. McKay, Some computational results on the spectra of graphs, pp. 73-92 of Combinatorial Mathematics IV (Adelaide 1975), Lect. Notes Math., 560 (1976).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| 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).
E. Spence, Numbers of characteristic polynomials and cospectral graphs for A
Eric Weisstein's World of Mathematics, Determined by Spectrum
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CROSSREFS
| Cf. A178925 (simple graphs determined by spectrum).
Sequence in context: A003222 A003167 A062412 * A066205 A113147 A206154
Adjacent sequences: A006605 A006606 A006607 * A006609 A006610 A006611
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KEYWORD
| nonn,hard,more
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| a(10) from Eric W. Weisstein (eric(AT)weisstein.com), Dec 30 2010
Two more terms from Ruperto Corso (rupertocorsoto(AT)gmail.com), Dec 18 2011
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