Return all possible factor combinations of a number (factors must be >= 2).
Return all possible combinations of factors (numbers >= 2) that multiply to the given integer n. Each combination should be in ascending order. The result should not include 1 or n itself.
Examples
Input:12
Output:[[2,6],[2,2,3],[3,4]]
Input:37
Output:[]
Hints
Use backtracking to find all factor combinations.
Start with factors from 2 up to sqrt(n).
Ensure factors in each combination are in non-decreasing order.