Consider the prime factorization of 1000:

We see that the prime factorization of 1000 contains 5 repeating three times and 2 repeating three times.
We can keep 5 repeating 3 times,
We can write a prime whose square is larger than

, for example:

Then we can write any prime which does not repeat, for example 2.
Thus the number we formed is

Answer: 12,250