The graph with spectrum 141 240 (−4)10 (−6)9
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We show that there is a unique graph with spectrum as in the title. It is a subgraph of the McLaughlin graph. The proof uses a strong form of the eigenvalue interlacing theorem to reduce the problem to one about root lattices.
KeywordsGraph spectrum Strongly regular graph Root lattice
Mathematics Subject Classification (2000)05C50 05E30 05C62
© The Author(s) 2011