I once saw another example coin like this where the "useful PoW" was finding chains of prime numbers or something. However, PoW solutions were not dependent on

I once saw another example coin like this where the "useful PoW" was finding chains of prime numbers or something. However, PoW solutions were not dependent on the current blockchain sate, which rendered it insecure as someone could just stockpile solutions and then hijack the blockchain. Is it the case here too? The closest I've seen to a useful PoW coin is one which relied in intel SGX to prove that the work done was useful and honest, but of course the central root of trust is really Intel's SGX in that case.