Factor Combinations

Numbers can be regarded as product of its factors. For example,

8 = 2 x 2 x 2;
  = 2 x 4.

Write a function that takes an integer n and return all possible combinations of its factors.
Note:

1. Each combination's factors must be sorted ascending, for example: The factors of 2 and 6 is [2, 6], not [6, 2].
2. You may assume that n is always positive.
3. Factors should be greater than 1 and less than n.

Examples:
input: 1
output:

[]

input: 37
output:

[]

input: 12
output:

[
  [2, 6],
  [2, 2, 3],
  [3, 4]
]

input: 32
output:

[
  [2, 16],
  [2, 2, 8],
  [2, 2, 2, 4],
  [2, 2, 2, 2, 2],
  [2, 4, 4],
  [4, 8]
]

public class Solution {
    public List<List<Integer>> getFactors(int n) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        if (n <= 2) {
            return res;
        }
        helper(n, 2, new ArrayList<Integer>(), res);
        return res;
    }
 
    private void helper(int n, int fc, List<Integer> list, List<List<Integer>> res) {
        if (list.size() >= 2 && n == 1) {
            List<Integer> newList = new ArrayList<Integer>(list);
            res.add(newList);
        }
        for (int i = fc; i <= n; i++) {
            if (n % i == 0) {
                list.add(i);
                helper(n / i, i, list, res);
                list.remove(list.size() - 1);
            }
        }
    }
}
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