A099881 Number of pairs of n-node simple graphs that are isospectral (excluding triples, etc.).

0, 0, 0, 0, 1, 5, 52, 771, 21025

Offset

1,6

Links

Table of n, a(n) for n=1..9.

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

Eric Weisstein's World of Mathematics, Isospectral Graphs

Crossrefs

Cf. A099882, A006608.

Sequence in context: A193809 A134111 A071583 * A280063 A363356 A365012

Adjacent sequences: A099878 A099879 A099880 * A099882 A099883 A099884

Keyword

nonn,more

Author

Eric W. Weisstein, Oct 28 2004

Status

approved