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Number of n-node forests not determined by their spectra.
(Formerly M1273)
0

%I M1273 #17 Mar 31 2022 22:00:03

%S 0,0,0,0,0,2,4,14,38,89,234,581,1471,3560,8940,21229,52876,126393,

%T 309993

%N Number of n-node forests not determined by their spectra.

%C Table 9 of Godsil and McKay gives incorrect a(12) = 579 and a(13) = 1466 (also has incorrect total number of forests). - _Sean A. Irvine_, May 15 2017

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

%H C. Godsil and B. D. McKay, <a href="http://doi.org/10.1007/BFb0097370">Some computational results on the spectra of graphs</a>, pp. 73-92 of Combinatorial Mathematics IV (Adelaide 1975), Lect. Notes Math., 560 (1976).

%H Jürgen Jost, Raffaella Mulas, and Leo Torres, <a href="https://arxiv.org/abs/2203.10824">Spectral theory of the non-backtracking Laplacian for graphs</a>, arXiv:2203.10824 [math.SP], 2022.

%Y Cf. A005195.

%K nonn

%O 1,6

%A _N. J. A. Sloane_.

%E a(12) and a(13) corrected and a(14)-a(19) from _Sean A. Irvine_, May 15 2017