Erdős problem 429
Is it true that, if is sparse enough and does not cover all residue classes modulo for any prime , then there exists some such that is prime for all ?
Sources
FormalConjectures/ErdosProblems/
429.lean
Retained formal statement
Is it true that, if is sparse enough and does not cover all residue classes modulo for any prime , then there exists some such that is prime for all ?
Weisenberg [We24] has shown the answer is no: can be arbitrarily sparse and missing at least one residue class modulo every prime , and yet is not contained in the primes for any . (Weisenberg gives several constructions of such an .)
False ↔ ∃ f, Filter.Tendsto f Filter.atTop Filter.atTop ∧ ∀ (A : Set ℕ), A.Infinite → (∀ (N : ℕ), (A ∩ Set.Icc 1 N).ncard ≤ f N) → (∀ (p : ℕ), Nat.Prime p → ∃ b, ∀ a ∈ A, ↑a ≠ b) → ∃ n, ∀ a ∈ A, Nat.Prime (n + a)