Editing Quadratic residue (section)

===Graph theory===

[[Paley graph]]s are dense undirected graphs, one for each prime ''p'' ≡ 1 (mod 4), that form an infinite family of [[conference graph]]s, which yield an infinite family of [[symmetric matrix|symmetric]] [[conference matrix|conference matrices]].

Paley digraphs are directed analogs of Paley graphs, one for each ''p'' ≡ 3 (mod 4), that yield [[Skew-symmetric matrix|antisymmetric]] conference matrices.

The construction of these graphs uses quadratic residues.