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A006608 Number of n-node graphs not determined by their spectrum.
(Formerly M1981)
0, 0, 0, 0, 2, 10, 110, 1722, 51039, 2560606, 215331676, 31067572481 (list; graph; refs; listen; history; text; internal format)



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


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. 73-92 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


Cf. A178925 (simple graphs determined by spectrum).

Sequence in context: A240625 A062412 A212491 * A066205 A113147 A206154

Adjacent sequences:  A006605 A006606 A006607 * A006609 A006610 A006611




N. J. A. Sloane.


a(10) from Eric W. Weisstein, Dec 30 2010

Two more terms from Ruperto Corso, Dec 18 2011



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Last modified December 9 15:04 EST 2019. Contains 329877 sequences. (Running on oeis4.)