Example 2 Proof: There exists an increasing sequence of positive integers , such that for any , the sequence contains at most a finite number of prime numbers.
Solution
Let denote all prime numbers in ascending order.
Now, we construct the sequence that meets the requirements.
Let , and suppose have been determined. Take as the smallest positive integer greater than that satisfies the following system of congruences:
Note that the Chinese Remainder Theorem guarantees the existence of such an .
We claim that the sequence defined by the above recursion satisfies the problem's requirements. For any , when , we have . Combining this with the fact that is increasing, it follows that every term of from the -th term onward is a multiple of and is greater than . Therefore, has at most prime terms.
The proposition is thus proved.
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