## Factorial

Factorial can be defined recursively as `f(n) = n*f(n-1)`

, with a base case value of `f(0) = 1`

.

Your task is to write a function `factorial`

which takes a single number `n`

and returns `f(n)`

.

Factorial can be defined recursively as `f(n) = n*f(n-1)`

, with a base case value of `f(0) = 1`

.

Your task is to write a function `factorial`

which takes a single number `n`

and returns `f(n)`

.