What is Ermmmmm? What about m? If you tell me, then I’ll figure out what it is.

Haha … very funny! If y! is 40320, then what is y? Obviously, it’s 8. It’s probably a hard question to inverse a factorial. For example, if x! is 2432902008176640000, then what is x? It’s 20.

! are used everywhere. The number e can be expressed as this:

{\displaystyle e=\sum \limits _{n=0}^{\infty }{\frac {1}{n!}}={\frac {1}{1}}+{\frac {1}{1}}+{\frac {1}{1\cdot 2}}+{\frac {1}{1\cdot 2\cdot 3}}+\cdots }

It literally means that the sum of all reciprocals of all factorials.

!s are also used in Permutation/Combinatorics, Calculus, Probability Theory, etc. Also:

{\displaystyle \ln n!=\sum _{x=1}^{n}\ln x\,.}

If you don’t know what ln means, go back to that old e post. And by the way, this is the end of the journey towards !s.



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