for a POW algorithm to be useful for blockchain verification it must be

 - hard to derive (for transaction verifiers)
 - controllable difficulty (so as more nodes are added, the difficulty can rise)
 - easy to prove (for relaying nodes)

hash algorithms are good here.  An algorithm with primes sounds like it would be based around the factorising problem (e.g. as used in RSA) - but the question is how Sunny has designed it to be variable - perhaps the difficulty is set by the length of required prime in bits, and the POW is two primes and a factor that meet the difficulty.  This would be very very ASICable compared with scrypt, but I don't think any off the shelf ASIC cores would exist (unlike with SHA256)

Interested to see what Sunny has come up with here.

Will