Question

What is another expression for the factorial of `n`?

Answer 1

Factorial `n`, or `n!` means:
Multiply all numbers from 1 up to and including `n`

Explanation:

Just as we have a summation sign `Sigma` (greek letter S for sum), there is also a multiplication sign `Pi` (greek P for product)

The expression would then be:

`n! = prod _(k=1)^n k`

Meaning: multiply all numbers `k`, varying from `1` to `n`.

The `!`-notation is more compact, but the `Pi`-notation can be used for a lot of other purposes.