162. Find a perfect number of the form $p q$, where $p$ and $q$ are prime numbers.
162. $\frac{\left(p^{2}-1\right)\left(q^{2}-1\right)}{(p-1)(q-1)}-p q=p q, \quad q=1+\frac{2}{p-1}, \quad$ from here $p_{1}=2, p_{2}=3, q_{1}=3, q_{2}=2$.

Answer. 6 .

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