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: You may assume that n is always positive. 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] ]