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Primecoin is a cryptocurrency based on finding prime numbers. Identifying prime numbers plays a central role in cryptography. Primecoin's unique Proof-of-Work (PoW) consensus mechanism is able to increase transaction speeds and improve energy efficiency.
The network searches for special prime number chains known as Cunningham chains and bi-twin chains, which are of interest in mathematical research.

HappyCoin is a Thai digital currency. It is designed to be used as a medium of exchange within Thailand. HappyCoin (HPC) has a hybrid consensus mechanism that combines elements of Proof-of-Work (PoW) and Proof-of-Stake (PoS).