Clarke's right, you should use Google more often. But what the heck, I can't resist the chance to show off my maths/physics knowledge: it's by far the largest number ever seriously used in mathematics (it is the upper limit of the answer to Graham's problem, which I won't pretend to understand). If you counted up every single particle in the universe, it would be a tiny fraction of Graham's number. In fact, I'm not sure anyone can even begin to imagine how large it is. Here's an explanation of it: http://www-users.cs.york.ac.uk/susan/cyc/g/graham.htmOriginally Posted bycrazyman2