I believe this problem is to safeguard against cheating.

This below formula can be useful (frankly, I don't know it if not for wikipedia): n! ~ sqrt(2*pi*n) * (n/e)^n However, this approximation only yields ~146, while the correct answer should be 148.41

How can someone expect people to answer that ?

Anybody know how to do this?

This question is truly obnoxious but if you have a good memory its doable. To calculate e^n you need to remember the expansion of the exponential. e^x = 1 + x +x^2/2! + x^3/3!+x^4/4! +x^5/5! + .... The term x^n/n! starts decaying when x>n so to do e^5 you need at least 5 terms, more likely 7 (this is why it is obnoxious to do without a pen and paper).

yeah, I wouldn't want to work for a company like that.