Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-oxford/2021/prelims/mathematics-ii/2/c/solution

The sequence does not converge. For , the largest prime factor is , while the sum of prime factors with multiplicity is . This subsequence therefore has ratio .
There are infinitely many prime numbers: if there were only , a prime factor of would be absent from the list. Listing the prime numbers in increasing order gives a subsequence of indices for which , so the ratio is constantly one. Every subsequence of a convergent sequence has the same limit of a sequence. The two distinct subsequential limits rule out convergence.

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