Status
On this page
Status
Topics
Status
On this page
Status
Topics
Let be minimal such that are mutually coprime.
Does, for every prime , the density of integers with exist? Does ? Is it true that if is the greatest prime such that and then ?
Let be minimal such that are relatively prime, that is, .
Does, for every prime , the density of integers with exist? Does ? Is it true, for every and all sufficiently large , that if is the greatest prime such that and then ?
Source: erdosproblems.com/770
No claim settles this problem.
The site's label is OPEN (page last edited 24 September 2025), and the standing derives from the claim pages: the only claim page, Zeng 2026, is partial, so the problem's standing is open, with no pending full claim. The historical bounds and unboundedness below do not answer the three questions. Erdős expected infinitely many , which would give a negative answer to the second question; that infinitude is itself unresolved in the sources this page cites. The partial claim settles the third implication for every fixed , but not for every positive .
The site's wording admits two degenerate readings. First, "mutually coprime" in its usual sense, every pair coprime, is met vacuously by the one-term list , so for every : the smallest instance is , where the collective gcd gives and the pairwise reading gives . On that reading the three questions are trivial, and the site's own remark that if and only if is prime fails at every with prime. Second, the third question carries no quantifiers; read for one fixed and every , it fails at for every (, ) and at for every (, , the example Zeng's listing gives), where is the greatest prime with . Both values of were checked by direct computation of the gcds. The change replaces "mutually coprime" by "relatively prime, that is, " and inserts "for every and all sufficiently large " in the third question; nothing else changes. The evidence is the poser's own text, Erdős (1974), Part II. On printed p. 199 Erdős defines as "the smallest integer for which the numbers are relatively prime" and says at once that when is prime and conversely, which holds only for the collective gcd; the unnumbered lemma on the same page, "The set of integers , is relatively prime", uses the phrase for the collective gcd, since for the list contains and , and the first divides the second. The site's commentary states the same equivalence. On printed p. 200 the third question reads "It is possible that if is large (say ) then ": the hypothesis is that be large, with for a fixed as the example of largeness, so the statement concerns large . The first defect is the site's ("mutually coprime" for Erdős's "relatively prime"); the missing quantifiers are already in Erdős's text. The formal-conjectures statement file, which counts with the site, reads the problem the same way. No result about either degenerate reading is recorded.