A099882 Number of triples of n-node simple graphs that are isospectral (excluding quadruples, etc.).

0, 0, 0, 0, 0, 0, 2, 52, 2015, 110812

Offset

1,7

Links

Table of n, a(n) for n=1..10.

Andries E. Brouwer, Numbers of characteristic polynomials and cospectral graphs for A.

P. E. John and Th. Ortlepp, Note on Cospectral Graphs with Simple Eigenvalues, MATCH, 48 (2003), 49-53. Give a(10)=110807, probably erroneously.

Eric Weisstein's World of Mathematics, Isospectral Graphs

Crossrefs

Cf. A099881, A006608.

Sequence in context: A297756 A174779 A215744 * A216611 A246485 A340837

Adjacent sequences: A099879 A099880 A099881 * A099883 A099884 A099885

Keyword

nonn,more

Author

Eric W. Weisstein, Oct 28 2004

Extensions

a(10) from Brouwer added by Andrei Zabolotskii, May 30 2026

Status

approved