# Euler Phi Function/Examples/16

## Example of Use of Euler $\phi$ Function

$\map \phi {16} = 8$

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

## Proof

$\map \phi {2^k} = 2^{k - 1}$

Thus:

$\map \phi {16} = \map \phi {2^4} = 2^3 = 8$

$\blacksquare$