I seem to recall once seeing a website that described various big numbers, such as the number of "distinguishable" mental states for a human brain, the number of distinguishable mental lives a person could have (where a mental life is defined as a succession of mental states, using some reasonable discretization of time), the number of different states a system the size of the known universe could have, the number of different histories such a universe could have, etc. (Of course there's a certain arbitrariness to the way one calculates these things, but still, the Ackerman-hierarchy complexity of these numbers is fairly insensitive to the details.) I also seem to recall that it was some post on math-fun that steered me toward that website, so can one of you point me in the right direction? Thanks, Jim Propp