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

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8 = 2 x 2 x 2
= 2 x 4

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

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

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Examples:

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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]
]