Euler Phi Function/Examples/9

Example of Use of Euler $\phi$ Function

 * $\map \phi 9 = 6$

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

Proof
From Euler Phi Function of Prime Power:
 * $\map \phi {3^k} = 2 \times 3^{k - 1}$

Thus:
 * $\map \phi 9 = \map \phi {3^2} = 2 \times 3 = 6$

They can be enumerated as:
 * $1, 2, 4, 5, 7, 8$