Primecoin is the first digital currency on the market that introduced a useful PoW, as opposed to Bitcoin's SHA256-based PoW. Primecoin uses searching prime numbers as a PoW. Not all types of prime number meet the requirements to be selected as PoW. Three types of prime numbers (known as Cunningham chain of the first kind, Cunningham chain of the second kind, and bi-twin chains) meet the requirements of a PoW algorithm to be used in cryptocurrencies.

The difficulty is dynamically adjusted via a continuous difficulty evaluation scheme in Primecoin blockchain. The efficient verification of PoW based on prime numbers is also of high importance, because if verification is slow, then PoW is not suitable. Therefore, prime chains are selected as a PoW because finding prime chains gets difficult as the chain increases in length whereas verification remains quick enough to warrant being used as an efficient PoW algorithm.

It is also important that once a PoW has been verified on a block, it must not be reusable on another block. This is accomplished in Primecoin by a combination of PoW certificates and hashing it with the header of the parent block in the child block.

The PoW certificate is produced by linking the prime chain to the block header hash. It also requires that the block header's origin be divisible by the block header hash. If it is, it is divided and after division, the quotient is used as a PoW certificate. Another property of the adjustable difficulty of PoW algorithms is met by introducing difficulty adjustment every block instead of every 2,016, as is the case with bitcoin. This is a smoother approach as compared to bitcoin and allows readjustment in the case of sudden increases in hash power. Also, the total number of coins generated is community-driven, and there is no definite limit on the number of coins Primecoin can generate.