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For which number theoretic functions is it true that, for any such that for almost all , there are infinitely many such that
For which number theoretic functions is it true that, for any with such that for almost all , there are infinitely many such that
Source: erdosproblems.com/122
No claim settles this problem.
Open. The site labels the problem OPEN (page last edited 2026-04-01) and its proof-claims tab carries no entry. The one claim page, Erdős's report of a proof for the divisor and prime-divisor counting functions, records a claimed partial answer with no published proof, so the derived standing is open.
The site's wording (accessed 2026-09-04; page last edited 2026-04-01) fails in two ways that the thread records. The site's revision of 2026-04-01 replaced by after thread comments of 2026-03-26 and 2026-03-27 showed that the earlier wording fails for every : a fast-growing , say , satisfies it and keeps the ratio bounded. The curator agreed on 2026-03-27 that [Er97] and [Er97e] carry the inverted ratio as a typo, while noting that [Er97] explicitly has the width of the interval tend to infinity faster than the normal order of , so the correction there is more than a typo. A thread comment of 2026-07-24 shows that the current wording, read literally with a positive integer and real-valued, fails for every positive-integer-valued : has , and contains no integer, so the count is zero for every ; that is a thread comment, not a claim. The change adds , the condition [Er97] carries as the curator describes it. The phrase "infinitely many such that the ratio tends to infinity" is read as a limit along a sequence of : some short intervals receive many more values of than their length. The site's commentary adds that [Er97] considers only growing more slowly than for some .