17. (3 points) As shown in the figure, small squares are arranged to form the following patterns. According to the arrangement rule, the 25th pattern requires how many small squares

将上面的文本翻译成英文，请保留源文本的换行和格式，直接输出翻译结果。
17. (3 points) As shown in the figure, the following shapes are formed using small squares. According to the placement pattern, the 25th shape requires $\qquad$ small squares.

【Analysis】Observation shows:
The first shape is composed of 1 square, i.e., $1^{2}$ squares;
The second shape is composed of $1+3=4$ squares, i.e., $2^{2}$ squares;
The third shape is composed of $1+3+5=9$ squares, i.e., $3^{2}$ squares;
The fourth shape is composed of $1+3+5+7=16$ squares, i.e., $4^{2}$ squares;

By analogy:
The $n$-th shape is composed of $1+3+5+7+\cdots+2n-1=n^{2}$ squares. The answer can be derived accordingly.
【Solution】Solution: According to the analysis:
The 25th shape requires small squares:
$$
\begin{array}{l} 
1+3+5+7+\cdots+49 \\
= 25^{2} \\
= 625 \text { (squares) }
\end{array}
$$

Answer: The 25th shape requires 625 small squares.
Therefore, the answer is: 625.
【Comment】The key to solving this problem is: correctly identifying the relationship between the number of the shape and the number of squares it contains, and then deriving their relationship.