The Largest Constructive Number: Graham's Number
Graham's number (named after Ronald Graham) is the biggest number that's been used constructively. However, it is too big to even begin to think about. It is "a large number that is an upper bound on the solution to a certain problem in Ramsey theory." Graham's number is so big that it's impossible even to discuss the number of digits within it—as well as the number of digits within that number.
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Key Facts In This Video
If you tried to picture Graham's number, your head would collapse into a black hole because your head cannot store the information required to imagine it. (0:30)
Three to the power of three to the power of three would be written as 3^(3^3), and the sum exceeds 7 trillion. (1:52)