\[\begin{array}{l} \varphi \left( n \right) = \sum\limits_{d|n} {d \cdot \mu \left( {\frac{n}{d}} \right)} {\text{,}} \hfill \\ {\text{где }}\mu \left( m \right){\text{ - функция Мёбиуса}} \hfill \\ \end{array}\]