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A named coined in 1938 by Milton Sirotta, the nine-year-old nephew of the mathematician Edward Kasner, when the child was asked by his uncle to come up with a name for a very large number; at the same time, googolplex was suggested for a still larger number. Kasner defined these numbers as follows:

   1 googol = 10100 (i.e. 1 followed by 100 zeros);
   1 googolplex = 10googol = 1010^100 (i.e. 1 followed by a googol number of zeros).

A googol is very roughly the number of years thought to be needed for all the black holes in the universe to evaporate by a process known as Hawking radiation. It is much larger than the number of protons and neutrons in the known universe (about 1080), but much smaller than the number of protons and neutrons needed to pack every cubic centimeter of the known universe (about 10128). The googolplex is the largest number with a proper name of which many people have heard. It is dwarfed, however, by such esoterica as Graham's Number.

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