This is a fantastic article on "big numbers" (and discusses tetration):
http://www.scottaaronson.com/writings/bignumbers.html
(I think someone has posted it to HN before, which is why I am leaving it as a comment)
http://www.scottaaronson.com/writings/bignumbers.html
(I think someone has posted it to HN before, which is why I am leaving it as a comment)
Shorter read: http://www.daviddarling.info/encyclopedia/K/Knuths_up-arrow_... , which comes quickly to next step:
Three up-arrows together represent a still more vastly powerful operator, equivalent to hyper5 or pentation, or a power tower of power towers
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