I assume you mean pseudo-random numbers. The simplest one I know (from writing videogames games back on old machines) worked like this:
seed=seed*5+1;
You do that every time random is called and then you use however many low bits you want. *5+1 has the nice property (IIRC) of hitting every possibility before repeating, no matter how many bits you are looking at.
The downside, of course, is its predictability. But that didn't matter in the games. We were grabbing random numbers like crazy for all sorts of things, and you'd never know what number was coming next.
Do a couple things like this in parallel, and combine the results. This is a linear congruential generator.
