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Let be a sequence such that . Suppose that the sequence of
contains infinitely many -tuples of consecutive values of which are all . Then (essentially)
where .
Let be a sequence such that . Suppose that the sequence of
contains infinitely many -tuples of consecutive values of which are all . Then, if is odd, are exactly the th roots of unity, and, if is even, they are the vertices of two regular -gons with the same circumscribed circle centred at the origin.
Source: erdosproblems.com/974
An accepted solution exists. The statement is true.
PROVED (LEAN). The site's label describes the precise Statement. The site credits Tijdeman [Ti66], who proved the stronger form with two runs of vanishing power sums, and it notes an independent proof in its thread. Its Lean marker refers to third-party formalizations that this corpus has not built. The standing derives from Tijdeman's claim page (1966).
The word "(essentially)" is Erdős's: [Er65b], printed p. 213, display
(37), reports the conjecture as Turán's, told to Erdős in conversation, and
leaves the word undefined; the site's commentary records that Erdős does not
elaborate on what it may mean. Read as the site words it, with the conclusion
that the are the th roots of unity, the conjecture fails for every even
: , gives , which vanishes for every
(Quanyu Tang, site thread, 20 September 2025), and for
the th roots of unity together with their rotation by give
for every , a run of zeros in every
period of length (Tao Hu's construction, posted by Tang the same day). The
site's curator, Thomas Bloom, resolves the word through Tijdeman's theorem. The
commentary (page last edited 1 October 2025) states the conclusion as "if is
odd then the must be exactly the th roots of unity, and if is even
they must be the vertices of two regular -gons with the same
circumscribed circle centred at the origin", credits Tijdeman [Ti66] and labels
the problem PROVED (LEAN); replying to the example in the thread on 20
September 2025, Bloom wrote that it "is not a counterexample though", given how
vaguely the problem is described; and the formal-conjectures statement
erdos_974, which the site's Lean mark follows, concludes that configuration.
The precise Statement replaces "(essentially) " by that conclusion
and changes nothing else. Under it the problem is proved: Tijdeman [Ti66] proves
the classification from two runs of vanishing power sums for pairwise
distinct , and a single run already forces the to be distinct and
nonzero (Proposition 1 of Hu, Tang and Zhang in the thread, proved in both Lean
files). Under the site's wording the answer is yes for odd , where the two
readings agree, and no for every even , by the construction above, which has
no claim page; its authors went on to treat the classification as the problem's
resolution. Erdős's setting in [Er65b] also requires for
, which the site's wording omits; neither answer changes, since the
conclusion forces and the construction lies on the unit circle.
Unread: Turán's own statement of the conjecture, and its statement in [Ti66].