LECTURE NOTES IN ANALYSIS (2011)
《LECTURE NOTES IN ANALYSIS (2011)》 · 第 97 页 · Section 2.8「Primitive Roots and Power Residues」，Definition 2.6
Let $m$ denote a positive integer and $a$ any integer such that $(a,m)=1$. Let $h$ be the smallest positive integer such that $a^h=1\pmod m$. We say that the order of $a$ modulo $m$ is $h$.