Twin prime conjecture
Very hardtwin-primes
Statement
Prove that there are infinitely many primes such that is also prime, i.e., where denotes the -th prime. A natural quantitative surrogate is the unconditional bound on .
Current frontier
Unconditionally H_1 ≤ 246 (Polymath 8b, 2014, building on Zhang 2013 and Maynard 2014); conditional on the generalized Elliott-Halberstam conjecture, H_1 ≤ 6.
When this counts as solved
A full solve is a rigorous proof that (the full twin prime conjecture), or a rigorous proof that twin primes are finite. A strict improvement also counts as a breakthrough: a complete unconditional proof of for some integer , a strict improvement of the EH-conditional bound below , or a complete unconditional proof of any case of Dickson's prime -tuples conjecture currently open. The improvement has to be a specific named integer, not asymptotic — sieve refinements that don't strictly lower don't count.
Classification
quantitative