Seonglae ChoFermat–Euler theorem, Euler's totient theorem
The theorem is further generalized into Carmichael's theorems
Euler's theorem
In number theory, Euler's theorem (also known as the Fermat–Euler theorem or Euler's totient theorem) states that, if n and a are coprime positive integers, then
a
φ
(
n
)
{\displaystyle a^{\varphi (n)}}
is congruent to
1
{\displaystyle 1}
modulo n, where
φ
{\displaystyle \varphi }
denotes Euler's totient function; that is
https://en.wikipedia.org/wiki/Euler's_theorem