XPM Primecoin

Primecoin (XPM) is a digital currency that runs on its own proof-of-work blockchain, originally created by Sunny King, a developer also known for PPCoin and early work on proof-of-stake. Rather than using the traditional hashing-based mining algorithm found in most cryptocurrencies, the network requires miners to search for chains of prime numbers, known as Cunningham and bi-twin chains, as the work that secures the chain and issues new coins. Because of this design, the energy spent mining Primecoin produces a secondary scientific output: the prime chains discovered during mining can be of interest to mathematical research, making the network "energy-multiuse" compared to proof-of-work systems whose computation has no external application. The protocol is built to balance sustained mining participation with a controlled supply schedule aimed at long-term scarcity. Its block targeting is significantly faster than Bitcoin's, allowing transactions to be confirmed in a fraction of the usual time. As a category, Primecoin sits within proof-of-work cryptocurrencies and is frequently cited as an early example of a useful-work mining scheme, prioritizing a mathematically meaningful consensus mechanism over conventional hash-based security.