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The ! symbol is used to represent the factorial operation.
The ! symbol is used to represent the factorial operation.


When a factorial appears inside a sentence, it's possible to misinterpret the ! as an exclamation mark:
When a factorial appears inside a sentence, it's possible to misinterpret the ! as an exclamation mark<ref>[https://twitter.com/matthras/status/1415236669553274882 Tweet by Matt Mack]</ref>:


<blockquote>
<blockquote>
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Two ! symbols together represent the ''double factorial'', multiplying just the odd or even numbers. So juxtaposition doesn't represent composition here: \(x!! \neq (x!)!\)
Two ! symbols together represent the ''double factorial'', multiplying just the odd or even numbers. So juxtaposition doesn't represent composition here: \(x!! \neq (x!)!\)
Does it make it clearer that a factorial is a present if you add another punctuation symbol after the ! symbol?
<blockquote>
"There are 6!."
</blockquote>
However, if you want to express surprise with an exclamation mark, it could look like a double factorial:
<blockquote>
"There are 6!!"
</blockquote>
Maybe ! should only be used for "factorial" in contexts that are unambiguously and clearly delimited mathematical notation, and the word "factorial" should be used in prose:
<blockquote>
"There are 6 factorial."
</blockquote>

Revision as of 09:20, 14 July 2021


The ! symbol is used to represent the factorial operation.

When a factorial appears inside a sentence, it's possible to misinterpret the ! as an exclamation mark[1]:

"How many ways of ordering six objects are there?"

"There are 6!"

Two ! symbols together represent the double factorial, multiplying just the odd or even numbers. So juxtaposition doesn't represent composition here: \(x!! \neq (x!)!\)

Does it make it clearer that a factorial is a present if you add another punctuation symbol after the ! symbol?

"There are 6!."

However, if you want to express surprise with an exclamation mark, it could look like a double factorial:

"There are 6!!"

Maybe ! should only be used for "factorial" in contexts that are unambiguously and clearly delimited mathematical notation, and the word "factorial" should be used in prose:

"There are 6 factorial."