Random numbers are divided into true random numbers and pseudo-random numbers. While true random numbers are based on natural events, pseudorandom numbers are generated by pseudorandom number generators (PRNG).
Pseudorandom number generators are software programs used to generate pseudorandom numbers. Many pseudorandom programs generate long sequences of digits from decimal numbers. In these digit sequences, which consist of the digits 0 to 9, the order and frequency of the decimal numbers varies purely randomly. The sequence of digits used to generate a pseudorandom number cannot be replicated by an attacker because the pseudorandom number generator is initialized with a true random event, such as noise or radioactive decay, called a "seed."
A well-known pseudorandom number generator is the Blum-Blum-Shub generator developed by Lenore Blum, Manuel Blum and Michael Shub.