Status
On this page
Status
Topics
Status
On this page
Status
Topics
Is it true that for every there exists a such that the density of for which
is at least (where is the greatest prime divisor of )?
Is it true that for every there exists a such that the lower density of for which
is at least (where is the greatest prime divisor of )?
Source: erdosproblems.com/1201
A full solution has been claimed but not yet accepted. The statement is true.
OPEN: the site's label, with the explanation that the question cannot be settled by a finite computation; the site's commentary records that Erdős wrote of having a proof of the case . The problem has no entry on the proof-claims tab, but the site's thread carries Przemek Chojecki's note of 2026-04-30, posted as written by GPT-5.5 Pro, which deduces the precise Statement from the Matomäki--Radziwiłł theorem and is recorded as a pending full claim on Chojecki's claim page (2026), and Chojecki's conditional natural-density note of 2026-05-01, also posted as written by GPT-5.5 Pro, recorded as a rejected claim on the conditional page, since it reaches the natural-density variant, and through it the precise Statement, only under an unproven hypothesis and only for . The site has accepted neither. The 30 April note is a pending full claim on the precise Statement, not accepted by the site, so the derived standing departs from the label: it is claimed, with the value proved.
The site's wording does not say which density it asks for: "the
density of ... is at least " can ask that the set of such have
an asymptotic density and that it be at least , or only that its lower
density be at least , and the two readings differ for a set whose
density need not exist. The change inserts "lower" before "density"; nothing
else changes. Erdős printed the question without a qualifier. [Er80], Section
6, item 2, printed p. 107 (library card:
Erdos 1980),
asks whether "the density of integers " for which the largest of
exceeds "is greater than "; the
same survey writes "lower density" where it means it, in a statement of the
same shape (printed p. 96, Gallagher's theorem on integers of the form
), so Erdős's text is consistent with either reading
and fixes neither. The reading is the site's curator's. In the site's thread
Will Sawin wrote (1 May 2026) that it is reasonable to read "density at least"
as "lower density at least" and "density at most" as "upper density at most"
rather than requiring a proof that the density exists, and Thomas Bloom
replied the same day: "I agree; I think this is generally how Erdős used these
terms. (When he was specifically curious about the existence of the density he
was generally clear about this.) I've tried to update all the problem
descriptions to reflect this, but missed this one." Bloom's evidence is
Erdős's general usage, and Bloom states the reading as the one the site's
problem descriptions are meant to carry. The formal-conjectures statement
erdos_1201 reads the bound the same way, as a liminf of the counting
ratio. Erdős's form differs from the site's in two further ways, the omission
of and "greater than" in place of "at least"; neither changes the
answer under the precise Statement, as the Formulation shows. Under the
precise Statement the answer is yes, pending acceptance: Chojecki's note of 30
April 2026, recorded on
its claim page (Chojecki, 2026), deduces
from the Matomäki--Radziwiłł theorem that the exceptional set has upper
density tending to as grows. Under the natural-density reading the
question is open: Terence Tao wrote in the thread (30 April 2026) that the
problem "remains technically open because it was not established that the
natural density of the set actually exists"; Chojecki's second note (1 May
2026), recorded on
its page, gives the
natural density only under an unproven
correlation hypothesis it names LPD and only for ; through that
reading it reaches the precise Statement only in that range and only under the
hypothesis, which the 30 April note already covers, so it does not count toward
the problem's standing; and the logarithmic-density results of Teräväinen that
Tao cited settle neither reading.