8.7 For an integer $n>3$, we use $n$ ? to denote the product of all primes less than $n$ (called “$n$-question mark”). Solve the equation $n ?=2 n+16$.


The equation in the problem is
$$
n ?-32=2(n-8) \text {. }
$$

Since $n$ ? cannot be divisible by 4, it follows from equation (1) that $n-8$ is odd. Suppose $n>9$, then $n-8$ has an odd prime factor $p$. Since $p2.9+16$. 7 is clearly a root of our equation. However, when $n=5$, we have $n ?=6<2 \times 5+16$. Therefore, our equation has a unique root $n=7$.