A006611 Number of n-node forests not determined by their spectra. (Formerly M1273)

0, 0, 0, 0, 0, 2, 4, 14, 38, 89, 234, 581, 1471, 3560, 8940, 21229, 52876, 126393, 309993

Offset

1,6

Comments

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

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..19.

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).

Jürgen Jost, Raffaella Mulas, and Leo Torres, Spectral theory of the non-backtracking Laplacian for graphs, arXiv:2203.10824 [math.SP], 2022.

Crossrefs

Cf. A005195.

Sequence in context: A333892 A135960 A216630 * A007462 A053623 A035010

Adjacent sequences: A006608 A006609 A006610 * A006612 A006613 A006614

Keyword

nonn

Author

N. J. A. Sloane.

Extensions

a(12) and a(13) corrected and a(14)-a(19) from Sean A. Irvine, May 15 2017

Status

approved