What's a Septillion?

There are 25 ways your show could start. The next time you ask them what they want next, there's only 24 left. So to work it out, I just multiplied 25 options to start times 24 times 23 and then all the numbers smaller until I got to one. And in maths we call that a factorial. It's got a name. In my show I talk about factorials and so I calculated 25 exclamation mark. So shouty 25. If you try and assign all the names, it's 15 Septillion, 511, Sextillion, 210, quintillion, 43 quadrillion, 330 trillion, 985 billion and 984 million. On average