Sierpiński-Riesel Base 5
Sierpiński-Riesel Base 5 tries to prove that k=159986 is the smallest possible Sierpiński number base 5 and that k=346802 is the smallest possible Riesel number base 5. To prove this, one must find primes for all k below the smallest known number.
How to participate
Participants in either of the projects reserve a k in the forum, then use NewPGen to sieve and then LLR to PRP test (for primality). After that, users unreserve their k again if no primes are found. Instructions to the project can be found at OmbooHankvalds guidepages.
As of this moment (2019-04-23), there are 32 Sierpiński and 69 Riesel base 5 candidate k left, which need primes.