Euler Phi Function of 2

Theorem

 * $\map \phi 2 = 1$

where $\phi$ denotes the Euler $\phi$ function.

Proof
From Euler Phi Function of Prime:
 * $\map \phi p = p - 1$

As $2$ is a prime number it follows that:
 * $\map \phi 2 = 2 - 1 = 1$