Factorial (!)
 Usage
Notes
 Further Examples
Here is a table of the first 20 factorials.
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Here is a way to invert the factorial function. In other words, InverseFactorial[n!] gives n when n is a positive integer.
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This checks the result for the first  factorials.
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There is no integer k such that k!   +  .
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 has approximately  digits yet InverseFactorial returns the correct answer quickly.
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