A Bitcoin is not a prime number. A Bitcoin is a digital asset and a payment system invented by Satoshi Nakamoto.
Transactions are verified by network nodes through cryptography and recorded in a public dispersed ledger called a blockchain. Bitcoin is unique in that there are a finite number of them: 21 million.
Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services.
As of February 2015, over 100,000 merchants and vendors accepted bitcoin as payment.
The unit of account of the bitcoin system is a bitcoin. Ticker symbols used to represent bitcoin are BTC and XBT. Its Unicode character is ₿. Small amounts of bitcoin used as alternative units are millibitcoin (mBTC), and satoshi (sat).
Named in homage to its creator, satoshi nakamoto, one satoshi is the smallest amount within bitcoin representing 0.00000001 bitcoins, one hundred millionth of a bitcoin.