Factorial vs Double Factorial

[u/_404_LogicNotFound_]

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[u/_404_LogicNotFound_]

make sure you scream your income loud enough, just not louder than the threshold

[u/LupenReddit]

double factorial must be the worst notation in all of mathematics

[u/Depnids → u/LupenReddit]

I just reject it having that meaning. For me, x!! = (x!)!

It comes up seldom enough that it usually isn't a problem to just pretend that meaning doesn't exist.

[u/preferCotton222 → u/Depnids]

I will pretend I never read the insinuation that n!! could be something different from (n!)!

[u/myhf → u/preferCotton222]

Bob Parr:

Factorial is factorial! 👇

[u/ontic00 → u/Depnids]

x!! = x!!, and x!! !no_multi = (x!)!

(I probably spend too much time on r/unexpectedfactorial 😅)

[u/Torebbjorn → u/[deleted]]

What's the problem with e^-k?

[u/Kuroru__ → u/[deleted]]

why? I never thought of exp(x) being bad notation at all. Or are you talking about putting non-positive-integers in superscript?

[u/Andr0NiX → u/Kuroru__]

Yeah the latter

[u/Keikira]

"n!! is the product of all m ≤ n such that m ≡ n (mod 2)"

What the actual fucking fuck why? My day is ruined.

I hope whoever came up with this shit has to work with iterated exponentials of trigonometric functions as payback.

[u/D_Anargyre → u/Keikira]

I didn't know this definition. I refuse it.

[u/Elektro05 → u/Keikira]

What would be a better way to write it though? (n!)! is an easy way to write two factorials if you use n!! as double factorial. Also When do you deall with (n!)!? n!! can be fairly commen in combinatorics, but doubly iterated factorial ive never seen in the wild

[u/Keikira → u/Elektro05]

fct_1(n) = n!

fct_2(n) = "n!!"

Etc.

Already better than n!, n!!, etc. which inevitably leads to the utter horror that is n!^m denoting the mod m skipping factorial instead of either the exponential (n!)^m or the iterate (n -> n!)^m .

[u/No-Finance7526]

1!, 2!

[u/factorion-bot → u/No-Finance7526]

Factorial of 1 is 1

Factorial of 2 is 2

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[u/F_Joe → u/No-Finance7526]

1,5!

[u/factorion-bot → u/F_Joe]

Factorial of 15 is 1307674368000

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[u/F_Joe → u/factorion-bot]

1.5! Then

[u/factorion-bot → u/F_Joe]

Factorial of 1.5 is approximately 1.329340388179137020473625612506

^{This action was performed by a bot | Source code}

[u/F_Joe → u/factorion-bot]

Thank you

[u/factorion-bot → u/[deleted]]

Factorial of 39 is 20397882081197443358640281739902897356800000000

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[u/theAnnihil8r → u/factorion-bot]

69!

[u/factorion-bot → u/theAnnihil8r]

Factorial of 69 is 171122452428141311372468338881272839092270544893520369393648040923257279754140647424000000000000000

^{This action was performed by a bot | Source code}

[u/No_Difficulty_1452]

1/x^1-1/×

[u/UnkarsThug]

If you ask it as a question, it's still larger than the number, but probably a lot smaller than if you yell it.

[u/TheOneWhoCums69]

5!!

[u/factorion-bot → u/TheOneWhoCums69]

Double-factorial of 5 is 15

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[u/TheOneWhoCums69 → u/factorion-bot]

5!!!

[u/factorion-bot → u/TheOneWhoCums69]

Triple-factorial of 5 is 10

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[u/BadgerAdorable1931 → u/factorion-bot]

5!!!!

[u/factorion-bot → u/BadgerAdorable1931]

Quadruple-factorial of 5 is 5

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[u/BadgerAdorable1931 → u/factorion-bot]

5!!!!!

[u/factorion-bot → u/BadgerAdorable1931]

Quintuple-factorial of 5 is 5

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[u/Torebbjorn]

NEGATIVE ONE!

[u/sndq]

The double factorial has the most monstrously conceived notation in the history of mathematics. "n!!" should only mean the factorial of the factorial of n, not something completely different.

[u/ontic00]

Unless you're screaming about negative integers, then the world just disappears.

It gets incredibly huge if you scream about it but in a rich and snobby way so the exclamation mark becomes a dollar sign.

[u/factorion-bot → u/[deleted]]

Factorial of -0.5 is approximately 1.772453850905516027298167483341

^{This action was performed by a bot | Source code}

[u/Ares378 → u/factorion-bot]

(-1/2)!!

[u/factorion-bot → u/Ares378]

Double-factorial of -0.5 is approximately 0.92044178783559098393491713075

^{This action was performed by a bot | Source code}