The following theorem was first proven by Pierre de Fermat (1601 – 1665). He proved it for prime numbers $p$ $$a^{p-1}(p)\equiv 1(p).$$ It is called **Fermat’s little theorem** to distinguish it from Fermat’s last theorem.

Later, this result was generalized by Euler, therefore, it is now called the Euler-Fermat theorem.

Let $m > 1$ be a positive integer and let $\phi(m)$ denote the Euler function. For any integer $a\in\mathbb Z$ which is co-prime to $m$ we have the congruence $$a^{\phi(m)}(m)\equiv 1(m).$$

| | | | | created: 2019-05-11 18:13:05 | modified: 2019-06-22 08:44:06 | by: *bookofproofs* | references: [1272]

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[1272] **Landau, Edmund**: “Vorlesungen über Zahlentheorie, Aus der Elementaren Zahlentheorie”, S. Hirzel, Leipzig, 1927