Given a positive integer n, return a list of its prime factors in ascending order with repetition. For example, 12 = 2 x 2 x 3, so the result is [2, 2, 3]. For values of n less than or equal to 1, return an empty list.
Examples:
Input: n = 12
Output: [2, 2, 3]
Explanation: 12 = 2 x 2 x 3
Input: n = 7
Output: [7]
Explanation: 7 is itself prime
Input: n = 1
Output: []
Explanation: 1 has no prime factors
Input: n = 100
Output: [2, 2, 5, 5]
Explanation: 100 = 2 x 2 x 5 x 5
Input: n = 30
Output: [2, 3, 5]
Explanation: 30 = 2 x 3 x 5
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