Answer: Pi is an important mathematical constant that appears in many mathematical, scientific, and engineering problems. In mental training, children's attention can be fully exercised. The number of hesitant pi is meaningless, irregular, and interconnected, making it more tedious compared to written content. Therefore, if memory is needed, it is necessary to concentrate. As the number increases, the time for memorization will also be longer, and the time required for concentration will be longer, which can fully exercise children's persistence in concentration.