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(unique?? random?? )prime numbers. never heard of such prime numbers

store all prime numbers in array in given range. and then use shuffle deck of cards case to print random number from the array

Assuming that you want a prime number in a given range. It is a known theorem that there are n/log(n) prime numbers till N.

So, given a and b, find the number of prime numbers(say p) from 1 to b, and also find the number of primes(say q) from 1 to a.

So, there are q-p prime numbers between a and b. So, for every (b-a)/(q-p), there should be a prime number, so try all numbers from a till a+( (b-a)/(q-p) ) and you should find one.