Euler Phi Function/Examples/9

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Example of Use of Euler $\phi$ Function

$\map \phi 9 = 6$

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

Proof

$\map \phi {3^k} = 2 \times 3^{k - 1}$

Thus:

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

They can be enumerated as:

$1, 2, 4, 5, 7, 8$

$\blacksquare$