Primecoin

Prime coin (sign: Ψ; code: XPM) is a cryptocurrency that implements a proof-of-work system that searches for chains of prime numbers.

Launched on 7th July 2013 by anonymous hacker and Peer coin founder Sunny King, Prime-coin was one of the first cryptocurrency to have a proof-of-work system with a practical use. Earlier cryptocurrencies, such as Bitcoin, were mined using algorithms that solved arbitrary mathematical problems, the results of which had no value or use outside of mining the cryptocurrency itself. Prime coin's algorithm, however, computed chains of prime numbers (Cunningham and bi-twin chains), the results of which were published on its block chain's public ledger, available for use by scientists, mathematicians, and anyone else. Use of a proof-of-work system to calculate chains of prime numbers was an innovation that produced useful results while also meeting the criteria for a proof-of-work system: it involved a calculation that was difficult to perform but easy to verify, and the difficulty was adjustable.

Shortly after its launch, some trade journals reported that the rush of over 18,000 new users seeking to mine Prime coin overwhelmed providers of dedicated servers.

Prime coin targets a block generation period of one minute rather than every ten minutes, changes difficulty every block rather than every 2016 blocks, and has a dynamic block reward that is a function of the difficulty. Prime coin transactions are confirmed approximately 8–10 times as fast as Bitcoin transactions.