A prime number is a number that is greater than "1" and is divisible only by "1" or itself. Prime numbers include the digits 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 53, etc, etc. They can be up to infinite powers of ten in length. So far, prime numbers with tens of millions of digits have been proven. The digit "1" is not considered a prime number.
Prime numbers are used in various encryption schemes. Some encryption algorithms like the DSA algorithm or the RSA method are based on the product of two prime numbers. As a result, conclusions about the two prime numbers are only possible with extremely high computational effort.