Berlekamp–Van Lint–Seidel graph

Summary

In graph theory, the Berlekamp–Van Lint–Seidel graph is a locally linear strongly regular graph with parameters $(243,22,1,2)$. This means that it has 243 vertices, 22 edges per vertex (for a total of 2673 edges), exactly one shared neighbor per pair of adjacent vertices, and exactly two shared neighbors per pair of non-adjacent vertices. It was constructed by Elwyn Berlekamp, J. H. van Lint, and Johan Jacob Seidel as the coset graph of the ternary Golay code.