There is (was?) one called riecoin that searched for dense clusters of primes.<p>I wrote a little about developing a miner for it I'm 2014: <a href="https://da-data.blogspot.com/2014/03/fast-prime-cluster-search-or-building.html" rel="nofollow">https://da-data.blogspot.com/2014/03/fast-prime-cluster-sear...</a><p>There's one called "nexus" that finds sparse clusters of primes of longer length than the ones in riecoin but where there can be a slightly larger inter-prime gap.<p>(It turns out to be a bad idea to use a mathematically complicated proof of work function, because it means someone like me will come along with some friends who are GPU programming experts and mine your coin better than the developer can.)
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Does anyone know other innovative PoW chains?<p>Wikipedia gives some ideas:<p><a href="https://en.wikipedia.org/w/index.php?title=Proof_of_work&oldid=1331709259#List_of_proof-of-work_functions" rel="nofollow">https://en.wikipedia.org/w/index.php?title=Proof_of_work&old...</a><p><a href="https://en.wikipedia.org/w/index.php?title=Proof_of_work&oldid=1331709259#Proof_of_useful_work_(PoUW)" rel="nofollow">https://en.wikipedia.org/w/index.php?title=Proof_of_work&old...</a><p>For example<p>* Cuckoo Cycle: <a href="https://docs.grin.mw/wiki/miscellaneous/cuckoo-cycle/" rel="nofollow">https://docs.grin.mw/wiki/miscellaneous/cuckoo-cycle/</a><p>* The paper "Ofelimos: Combinatorial Optimization via Proof-of-Useful-Work A Provably Secure Blockchain Protocol": <a href="https://crypto.iacr.org/2022/papers/538804_1_En_12_Chapter_OnlinePDF.pdf" rel="nofollow">https://crypto.iacr.org/2022/papers/538804_1_En_12_Chapter_O...</a><p>Quote from Wikipedia concerning Ofelimos: "At the IACR conference Crypto 2022 researchers presented a paper describing Ofelimos, a blockchain protocol with a consensus mechanism based on "proof of useful work" (PoUW). Rather than miners consuming energy in solving complex, but essentially useless, puzzles to validate transactions, Ofelimos achieves consensus while simultaneously providing a decentralized optimization problem solver. [...] The paper gives an example that implements a variant of WalkSAT, a local search algorithm to solve Boolean problems.|"
Monero's RandomX is an interesting PoW scheme one designed to be optimized for CPUs. Here is an interesting read about its design <a href="https://github.com/tevador/RandomX/blob/master/doc/design.md" rel="nofollow">https://github.com/tevador/RandomX/blob/master/doc/design.md</a><p>Chia uses a very memory-hard PoW system and is usually mined on SSDs.<p>I've seen a lot of "useful PoW" cryptocurrencies, but they tend to not pan out. For example Gridcoin is just a Proof-of-Stake cryptocurrency with a program that hands out GRC to BOINC contributors.