[ChainOfFools]

It may have been replaced by a cryptocurrency indeed, for there was PrimeCoin, one of the very few that actually did something that was both productive and unprofitable (critically important for the economics of mining) with its mining cycles, and that is look for prime numbers. Although I don't remember if these were Mersenne Primes. It was one of the very earliest altcoins and by its nature was CPU bound which made it unpopular with large scale mining farms, but extremely popular with CPU cycle thieves working in clueless corporate and educational IT departments.