From what I can tell your code is missing some key information. This is how to generate a random number.
Code:
Randomize
variable = Int((upperbound - lowerbound + 1) * Rnd() + lowerbound)
As far as keeping it to regenerate the same number, that would depend on how many digits your number is going to be. You would have to pass the variable to possibly a function to test it against a stored list of used values.