254. 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. You may assume that n is always positive.
2. Factors should be greater than 1 and less than n .

Example 1:

Input:

 
1

Output:

 []

Example 2:

Input:

 
37

Output:

[]

Example 3:

Input:

 
12

Output:

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

Example 4:

Input:

 
32

Output:

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