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Erdős problem 1209

Let A={a1<a2<}A=\{a_1<a_2<\cdots\} be a sequence of integers which tends to infinity sufficiently fast. If there is an nn such that all n+akn+a_k are primes then must there exist infinitely many such nn?

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1209.lean

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Let A={a1<a2<}A=\{a_1<a_2<\cdots\} be a sequence of integers which tends to infinity sufficiently fast. If there is an nn such that all n+akn+a_k are primes then must there exist infinitely many such nn?

Erdős [Er80] wrote 'unless I overlook a trivial way of getting a counterexample these questions are quite hopeless'. There is indeed a trivial counterexample (a variant of the construction in [erdosproblems.com/429]): define a1=2a_1=2 and for k2k\geq 2 let ak>ak1a_k>a_{k-1} be a prime such that ak+k0(modqk)a_k+k\equiv 0\pmod{q_k}, where qkq_k is some prime not dividing kk. This sequence can be made to grow arbitrarily fast

See also [erdosproblems.com/429] and [erdosproblems.com/1102].

FormalConjectures/ErdosProblems/1209.leanErdos1209.erdos_1209.parts.i5 linesExact file
Falsef,    ∀ (a : ℕ → ℕ),      StrictMono a        (∀ (k : ℕ), f ka k) → (∃ n, ∀ (k : ℕ), Nat.Prime (n + a k)) → {n | ∀ (k : ℕ), Nat.Prime (n + a k)}.Infinite
SolvedStatement only, no proof

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