Explanation

Lehmer Random Number Generator

https://en.wikipedia.org/wiki/Lehmer_random_number_generator

The Lehmer random number generator (named after D. H. Lehmer), sometimes also referred to as the Park–Miller random number generator (after Stephen K. Park and Keith W. Miller), is a type of linear congruential generator (LCG) that operates in multiplicative group of integers modulo n. The general formula is:

where the modulus m is a prime number or a power of a prime number, the multiplier a is an element of high multiplicative order modulo m (e.g., a primitive root modulo n), and the seed X0 is coprime to m.

Other names are multiplicative linear congruential generator (MLCG) and multiplicative congruential generator (MCG).