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Is there any way I can 'undo' the factorial operation? JUst like you can do squares and square roots, can you do factorials and factorial roots (for lack of a better term)?

Here is an example: 5! = 120. Is there a way I can work out the number that must be factorialed (??) to give the answer 120?

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    possible duplicate of [Is there an Inverse Gamma $\Gamma^{-1} (z) $ function?](http://math.stackexchange.com/questions/18362) and [Is there a way to solve for an unknown in a factorial?](http://math.stackexchange.com/questions/61755)2012-07-17

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You can just divide the "answer" by consecutive positive integers, and when the result is 1, the last number you divided by is the number that the "answer" is factorial of. For example: 120 / 2 = 60, 60 / 3 = 20, 20 / 4 = 5, 5 / 5 = 1, so the number that 120 is the factorial of is 5.

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    @digital-Ink Then I'd like to call these numbers perfect factorials.2015-12-27