Find all pairs (sets) of prime numbers (p,q) such that p*q <= n, where n is given number.

Example 1:
Input: n = 4
Output: 2 2
Explanation: Pair (2, 2) which has both prime
numbers as well as satisfying the condition
2*2 <= 4.
Example 2:
Input: n = 8
Output: 2 2 2 3 3 2
Explanation: Pairs(2, 2), (2, 3) and (3, 2)
which has both prime numbers and satisfying
the given condition.

Your Task:
You don't need to read or print anything. Your task is to complete the function prime_pairs() which takes n as input parameter and returns a list of pairs in ascending order.

Expected Time Complexity: O(n^{2}* sqrt(n))
Expected Space Complexity: O(1)

Constraints:
1 <= n <= 400

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