Well one blink at the implementation would show you that he CAN’T have any reason for that claim at all. Why? Because that’s how the set seed function looks like:
synchronized public void setSeed(long seed) {
seed = (seed ^ multiplier) & mask;
this.seed.set(seed);
haveNextNextGaussian = false;
}
And that’s exactly what’s called from the constructor. So even if you give it a prime, it won’t use it anyhow, so if at all you’d have to use a seed s where (s^ multiplier) & mask results in a prime 😉
Java uses a usual linear congruency method, i.e.:
x_n+1 = (a * x_n + c) mod m with 2 <= a < m; 0 <= c < m.
Since you want to get a maximal periode, c and m have to be relatively prime and a few other quite obscure limitations, plus a few tips how to get a practically useful version. Knuth obviously covers that in detail in part2 😉
But anyhow, the seed doesn’t influence the qualities of the generator at all. Even if the implementation would be using a Lehmer generator, it would obviously make sure that N is prime (otherwise the algorithm is practically useless; and not uniformly distributed if all random values would have to be coprime to a non prime N I wager) which makes the point moot