For which Natural $n\ge2: \phi(n)=n/2$ For which Natural $n\ge2$ does this occur with?: $\phi(n)=n/2$

$$n=\prod_{k=1}^rp_k^{a_k}\;\;,\;\;p_k\,\,\text{primes}\,\,,\,\,0<a_k\in\Bbb N\Longrightarrow$$
$$\phi(n)=n\prod_{k=1}^r\left(1-\frac{1}{p_k}\right)$$
and then
$$\frac{n}{2}=\phi(n)\Longleftrightarrow 2\prod_{k=1}^r\left(1-\frac{1}{p_k}\right)=1\Longleftrightarrow\ldots$$
Can you take it from here?
