I already know that, but I don't know what ∫ is.

Have you studied any calculus?

]]>What kind of calculator are you using? How many digits do you want the answers to be? Are you looking to calculate it? Then we would use series and recurrence relations. If you are trying understand it then the integral which is the definition is purely formal. You would need to numerically integrate to get any practical answer.

Also, remember that for negative integers the gamma function is undefined.

]]>You can use the fact that:

and numerically integrate.

]]>The gamma function isn't defined for negative integers. It is defined for decimals though, but in general, most of them aren't expressible in terms of known constants.

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