The resident genius that runs in my offline campaign does not like computer-driven random number generators. They do not, in his correct estimation, produce 'true' random numbers. The most flexible, familiar one on your system would be in your excel program, in which you can obtain a random number either by typing either formula:
=randbetween(x,y) - which will give you whole numbers between x & y
=rand()*x - which will give you all numbers between zero and x.
There are ways to play with these formulas, but I'll let you look it up elsewhere. I mean only to address the problem that these number generators (which use the clock in your computer as the initial 'seed') are only good for ONLY tens of thousands of random numbers. Hm. I don't know about you, but tens of thousands sounds like a lot.
If we presume that the time it takes to roll a die, watch it bounce on the table and stop, read the number, and snatch up the die preparatory to roll it again is only one-and-a-half seconds, it would take you four hours and ten minutes to roll the die 10,000 times. This is assuming the die never takes too long to roll, and never rolls far enough away that you need to lean forward (wasting precious tenths of a second) and that you never drop it. So, under those circumstances, it is possible to make 10,000 rolls in the space of an ordinary D&D session.
But even if we argue that the second set of 10,000 numbers is precisely the same as the first set (because we have a really crappy number generator), it hardly makes a difference ... because those die rolls will be applied to so many possible tables that the repetition becomes meaningless. The only concern would be that you or the players knew what the next number in the sequence was going to be - and that they modified their behavior to take advantage.
Try an experiment. Write out a list of 100 d20 rolls, print them and hand them to each player. Do not keep a list for yourself. If at all possible, don't look at the list you give your players. Tell your players that these are going to be the next rolls that everyone is going to you - DM included. Then run your game, designating when your players should roll dice to hit, save or whatever else as usual. Do not let your players choose the order in which they attack - go right to left around the table, or whatever usual method you use to keep order in your game.
I'm guessing that foreknowledge of the rolls won't be that much of an advantage. I'm also guessing the players will get frustrated at the enemy "stealing" their rolls. They might be able to strategize a little, since they will hold a physical list in their hands which they can think about in advance.
Imagine how hard it would be to make it work if they had only their memories to rely upon, and could not compare memories with each other.
The reality is that we're not complex enough to take advantage of a repetition even if there was one. If there was some Rain Man at the table with perfect memory, and he was restrained from shouting out the numbers ahead of time (I know a number of people who would like Hoffman gagged), he wouldn't have that much of an advantage, since those really good numbers were going to be stolen from him most of the time. Perhaps some genius would like to write and tell me how they'd manage it - for myself, I think that one more elf standing behind a tree taking one unexpected bow shot would totally fuck up Rain Man's whole plan.
Tell me how I'm wrong.
From my experience, I believe the game itself is unpredictable enough to counter-balance any lack of randomness that might be present in a pseudo number generator. There are too many human variables influencing the exact course of action from minute to minute that doesn't exist in the static computer codebreaker/statistics manager that needs 'real' random numbers.
Perhaps there's a future in cyphers based on four D&D players fighting a red dragon that the Russians are working on right now.
You can try this experiment too. Tell your players you're going to use a random number generator for every roll all night. Make lists of 150 x d20, d12, d10, d8, d6 and d4 rolls, and use that list over and over again - using multiples for when more than one die is rolled (3d4 for instance). Don't tell them you're doing this.
See if anyone notices a repetition. If they do, see if they can make use of it in the course of one session.
(You can always justify these things by handwaving their justification with magic)