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Number theory
Erdős problem 828 - lehmer conjecture
When n>1, Lehmer conjectured that ϕ(n)∣n−1 if and only if n is prime.
$2,251 bounty·1 piece from 1 person·last one 18 days ago
week of 28 Sept 2025 · nothing publishedweek of 5 Oct 2025 · nothing publishedweek of 12 Oct 2025 · nothing publishedweek of 19 Oct 2025 · nothing publishedweek of 26 Oct 2025 · nothing publishedweek of 2 Nov 2025 · nothing published
Solve it
A complete proof or refutation in Lean. The first one the validator accepts takes the whole bounty.
28 Sept 2025a year of work on this problem20 Sept 2026
erdosproblems.com/828
Something wrong with this formalization?
A statement that does not faithfully capture the original conjecture is the one real risk here, so we would rather hear about it early - before someone spends weeks on it.
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