Root prime gap
I recently found out about Andrica’s conjecture: the square roots of consecutive primes are less than 1 apart. In symbols, Andrica’s conjecture says that if pn and pn+1 are consecutive prime numbers, then √pn+1 − √pn < 1. This has been empirically verified for primes up to 2 × 1019. If the conjecture is true, it puts an upper bound on how long you’d have to search to find the next prime: pn+1 < 1 + 2√pn + […]