42. Factorize the number $989 \cdot 1001 \cdot 1007 + 320$ into prime factors.
87.42. Let's denote 991 by $x$ and rewrite the given expression

$$
\begin{gathered}
(x-2)(x+10)(x+16)+320=x^{3}+24 x^{2}-108 x= \\
=x(x+6)(x+18)=991 \cdot 997 \cdot 1009
\end{gathered}
$$

These three numbers are prime, and the factorization is complete.