A242953 Number of connected graphs on n vertices whose spectrum has fewer than n distinct eigenvalues.

0, 0, 1, 3, 10, 58, 314, 3798, 51609, 1716267

Offset: 1

Author

Travis Hoppe and Anna Petrone, May 27 2014

Keywords

• nonn
• more

Comments

The spectrum refers to the eigenvalues of the adjacency matrix.

Links

• Travis Hoppe and Anna Petrone, Encyclopedia of Finite Graphs
• T. Hoppe and A. Petrone, Integer sequence discovery from small graphs, arXiv preprint arXiv:1408.3644, 2014
• Eric Weisstein's World of Mathematics, Graph Spectrum

Crossrefs

Cf. A064731 (integral graphs), A242952 (distinct spectrum graphs).

Extensions

Corrected, original description as the "non-real spectrum" was incorrect, by Travis Hoppe, Mar 23 2015