What you need is what is called a linear feedback shift register,its not a random number generator as randomness is impossible in a deterministic system, they are used to produce psuedo random numbers,the numbersequences they produce have lots of interesting number theoretic properties but the most usefull is they can be made to produce sequences 2^N-1 bits long of seeminngly random numbers,but with no colisions.
a google search will give yu the pertinant facts
BTW,if you need true randomness the you have to use some natural source as your starting point,we use a reverse biased diode