In the mathematical field of graph theory, the triangle graph is a planar undirected graph with 3 vertices and 3 edges, in the form of a triangle.^[1]

Triangle graph
The triangle graph
Vertices	3
Edges	3
Radius	1
Diameter	1
Girth	3
Automorphisms	6 (D3)
Chromatic number	3
Chromatic index	3
Properties	2-regular Vertex-transitive Edge-transitive Unit distance Hamiltonian Eulerian
Notation	${\displaystyle C_{3}}$ or ${\displaystyle K_{3}}$
Table of graphs and parameters

The triangle graph is also known as the cycle graph ${\displaystyle C_{3}}$ and the complete graph ${\displaystyle K_{3}}$.