Euler Phi Function of 15

Example of Euler $\phi$ Function of Non-Square Semiprime

$\map \phi {15} = 8$

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

Proof

We have that:

$15 = 3 \times 5$

Thus:

\(\ds \map \phi {15}\)

\(=\)

\(\ds \paren {3 - 1} \paren {5 - 1}\)

Euler $\phi$ Function of Non-Square Semiprime

\(\ds \)

\(=\)

\(\ds 2 \times 4\)

\(\ds \)

\(=\)

\(\ds 8\)

$\blacksquare$