---
tag: 0VHJRXNAAS
kind: concept
name: Chromatic number
msc: [05C15]
sources:
  - url: https://en.wikipedia.org/wiki/Graph_coloring
    locator: Vertex coloring
---

## Summary

The chromatic number of a graph is the least number of colours in a proper colouring. It is a central invariant of graph theory, and the four colour theorem bounds it for planar graphs. The node [[chromatic number|0C5M7AM6FH]] gives the precise definition.