25. What is the maximum number of parts that $n$ planes can divide space into?
25. The maximum number of parts obtained by dividing space with $n$ planes is achieved under the condition that no two of these planes are parallel, no three pass through the same line or are parallel to the same line, and no four pass through the same point. Then $n$ planes can divide space into $\frac{n^{3}+5 n}{6}+1$ parts. The validity of this conclusion can be verified by the method of mathematical induction.