Opcodes that generate random numbers are:
See seed which sets the global seed value for all x-class noise generators, as well as other opcodes that use a random call, such as grain. And getseed returns the global seed value used for all x-class noise generators.
rand, randh, randi, rnd(x) and birnd(x) are not affected by seed. Use rndseed for that.
See also functions which generate random numbers in the section Random Functions.