User:Dereckson/Sandbox

$\varphi (n)=n\prod _{p\mid n}\left(1-{\frac {1}{p}}\right),$

$\varphi (p^{k})=p^{k}-p^{k-1}=p^{k-1}(p-1)=p^{k}\left(1-{\frac {1}{p}}\right).$

I267421