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JOURNALS // Sibirskie Èlektronnye Matematicheskie Izvestiya [Siberian Electronic Mathematical Reports] // Archive

Sib. Èlektron. Mat. Izv., 2021 Volume 18, Issue 2, Pages 1075–1082 (Mi semr1423)

Discrete mathematics and mathematical cybernetics

Distance-regular Terwilliger graphs with intersection arrays $\{50,42,1;1,2,50\}$ and $\{50,42,9;1,2,42\}$ do not exist

A. A. Makhneva, M. S. Nirovaba

a N.N. Krasovsky Institute of Mathematics and Meckhanics, 16, S. Kovalevskoy str., Ekaterinburg, 620990, Russia
b Kabardino-Balkarian State University named after H.M. Berbekov, 175, Chernyshevsky str., Nalchik, 360004, Russia

Abstract: Let $\Gamma$ be a distance-regular graph and its local subgraphs are isomorphic the Hoffman-Singleton graph. A.L. Gavrilyuk and A.A. Makhnev proved that $\Gamma$ is the Terwilliger graph with intersection array $\{50,42,9;1,2,42\}$ or $\{50,42,1;1,2,50\}$. In this paper we prove that Terwilliger graphs with intersection arrays $\{50,42,1;1,2,50\}$ and $\{50,42,9;1,2,42\}$ do not exist.

Keywords: distance-regular graph, Terwilliger graph, triple intersection numbers.

UDC: 519.17

MSC: 05C25

Received December 11, 2020, published October 20, 2021

DOI: 10.33048/semi.2021.18.82



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© Steklov Math. Inst. of RAS, 2025