function to approximate $x!$ without factorial

Question

I am looking for a function $f(x)$ such that $f(x)\approx x!$, but (obviously) the function of x does not use factorial, eg a polynomial or exponential function. it does not have to be precise, just somewhat close to the actual value. perhaps 2 functions, such that one gives a lower bound and one gives an upper bound, $f(x)<x!<g(x)$, would be good.

Answer 1

Stirling Approx?

$$\sqrt{2\pi}\ n^{n+1/2}e^{-n} \le n! \le e\ n^{n+1/2}e^{-n}$$