The equivalence classes modulo some n form a partition of the integers so you can use that to create a very efficient solution with very little code. Here is a

The equivalence classes modulo some n form a partition of the integers so you can use that to create a very efficient solution with very little code. Here is a neat explanation: https://preshing.com/20121224/how-to-generate-a-sequence-of-unique-random-integers https://preshing.com/20121224/how-to-generate-a-sequence-of-... If you need even better properties (eg cryptographically secure) you can also look at PCG with k-dimensional equidistribution: http://www.pcg-random.org/index.html http://www.pcg-random.org/index.html