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Someone told me this, but I dont get it. $$\Gamma (Happy Birthday + 1)$$ Why is this the way to greet a mathematician on his birthday with an excitement?

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    $\begingroup$ the gamma function extends $n!$, $\Gamma(n+1)=n!$ $\endgroup$
    – yoyo
    Aug 25, 2013 at 17:52

1 Answer 1

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The joke is that

$$\Gamma(n + 1) = n!$$

is the factorial function. So

$$\Gamma(\text{Happy Birthday} + 1) = \text{Happy Birthday}!$$

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    $\begingroup$ since when is Happy Birthday a natural number? $\endgroup$ Aug 25, 2013 at 17:52
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    $\begingroup$ @DominicMichaelis Well, one does generally celebrate on natural-number # of years... $\endgroup$ Aug 25, 2013 at 17:54
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    $\begingroup$ @DominicMichaelis I suppose that by the time one learns of the gamma function, one has stopped celebrating half birthdays ;) $\endgroup$
    – user61527
    Aug 25, 2013 at 17:56

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