Sorry, I thought you meant the machines would be doing "real" work on behalf of some person renting it, rather than making Mersenne primes. If you have a fixed

Sorry, I thought you meant the machines would be doing "real" work on behalf of some person renting it, rather than making Mersenne primes. If you have a fixed problem like that then of course it won't run out. The problem then is more economics, who has an incentive to discover more Mersenne primes?