Abstract:
There exist well-known distance-regular graphs $\Gamma$ of diameter 3 for which $\Gamma_3$ is a triangle-free graph. An example is given by the Johnson graph $J(8,3)$ with the intersection array $\{15,8,3;1,4,9\}$. The paper is concerned with the problem of the existence of distance-regular graphs $\Gamma$ with the intersection arrays $\{78,50,9;1,15,60\}$ and $\{174,110,18;1,30,132\}$ for which $\Gamma_3$ is a triangle-free graph.