Click the cat. It can take some time. 100000 factorial = 2.824229407960254E+456573
Recently, @JeeJeeHogMole724 has made a factorial calculator, but it uses a formula which involves pi and square roots and so is not that accurate (5! is 120, but it displays 119). This uses the actual formula, so it is guaranteed to be at least 99.999% accurate. I also added large number support, so it can handle numbers larger then 10^308.
