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  "body": "\n## Definition\n\nLet $G$ be a finite [[graph|0JD5C82QMB]].\nThe chromatic number $\\chi(G)$ is the smallest natural number $k$ such that $G$ is [[$k$-colourable|0Y7VDAX8Q3]].\n\n## Remarks\n\nFor the [[complete graph|03WKB2H474]], $\\chi(K_n) = n$. For the [[cycle graph|0QQ0F12962]] $C_n$, $\\chi(C_n)$ is $2$ if $n$ is even and $3$ if $n$ is odd.\nA [[greedy colouring|04AAKZNXHD]] shows that $\\chi(G) \\le \\Delta(G) + 1$, where $\\Delta(G)$ is the [[maximum degree|0KNAN9F27P]].\nThe chromatic number is at least the [[clique number|0WCKRBHFFD]].\n\n## Explanations\n\n### L1 human\n\nThe chromatic number is the least number of colours that you need to colour a graph properly.\nFor a map, it is the least number of colours that keeps neighbouring countries in different colours.\n",
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