Factorial/Examples/1

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Example of Factorial

The factorial of $1$ is $1$:

$1! = 1$


Proof

From the definition of factorial:

$n! = \ds \prod_{k \mathop = 1}^n k$

where $\prod$ denotes continued product.

When $n = 1$ we have:

\(\ds 1!\) \(=\) \(\ds \prod_{k \mathop = 1}^1 k\)
\(\ds \) \(=\) \(\ds 1\)

$\blacksquare$