Primecoin is a peer-to-peer digital cryptocurrency created by Sunny King (also created Peercoin). Primcoin differs from Bitcoin in that it implements a scientific processing proof of work system. Miners give out processing power not to do menial pointless task like Bitcoin or Litecoin, instead those processing powers were used to help search for chains of prime numbers composed of Cunningham chains and bi-twin chains. The finding of prime numbers can then be used for numerous scientific and mathematical applications.
Primecoin also features a high speed block generation time, fast transaction confirmations, smooth difficulty adjustment, and a self adjusting block reward.