Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2016/iii/paper-124/5/a/solution

One general form of the Erdős-Kac theorem is the following. Let be a real strongly additive arithmetic function, with for all primes, and define
If , then under the discrete uniform distribution on ,
Here the arrow denotes convergence in distribution and is the standard normal distribution. Equivalently, the probability of being at most tends to the standard normal distribution function for every real . Replacing by is equivalent, because the difference is bounded by .
This is a general bounded-prime-weight form, not just the special case . In that case the Mertens theorem for reciprocal primes gives and , so the classical prime-factor central limit theorem is

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