A **googol** is the large number 10^{100}. In decimal notation, it is written as the digit 1 followed by one hundred zeroes: 10,

The term was coined in 1920 by 9-year-old Milton Sirotta (1911–1981), nephew of U.S. mathematician Edward Kasner.^{[1]} Kasner popularized the concept in his 1940 book *Mathematics and the Imagination*.^{[2]} Other names for googol include **ten duotrigintillion** on the short scale, **ten thousand sexdecillion** on the long scale, or **ten sexdecilliard** on the Peletier long scale.

A googol has no special significance in mathematics. However, it is useful when comparing with other very large quantities such as the number of subatomic particles in the visible universe or the number of hypothetical possibilities in a chess game. Kasner used it to illustrate the difference between an unimaginably large number and infinity, and in this role it is sometimes used in teaching mathematics. To give a sense of how big a googol really is, the mass of an electron, just under 10^{−30} kg, can be compared to the mass of the visible universe, estimated at between 10^{50} and 10^{60} kg.^{[3]} It is a ratio in the order of about 10^{80} to 10^{90}, or at most one ten-billionth of a googol (0.00000001% of a googol).

Carl Sagan pointed out that the total number of elementary particles in the universe is around 10^{80} (the Eddington number) and that if the whole universe were packed with neutrons so that there would be no empty space anywhere, there would be around 10^{128}. He also noted the similarity of the second calculation to that of Archimedes in *The Sand Reckoner*. By Archimedes's calculation, the universe of Aristarchus (roughly 2 light years in diameter), if fully packed with sand, would contain 10^{63} grains. If the much larger observable universe of today were filled with sand, it would still only equal 10^{95} grains. Another 100,000 observable universes filled with sand would be necessary to make a googol.^{[4]}

The decay time for a supermassive black hole of roughly 1 galaxy-mass (10^{11} solar masses) due to Hawking radiation is on the order of 10^{100} years.^{[5]} Therefore, the heat death of an expanding universe is lower-bounded to occur at least one googol years in the future.

A googol is approximately *70!* (factorial of 70).^{[a]} Using an integral, binary numeral system, one would need 333 bits to represent a googol, i.e., 1 googol = ≈ 2^{332.19280949}. However, a googol is well within the maximum bounds of an IEEE 754 double-precision floating point type, but without full precision in the mantissa.

Using modular arithmetic, the series of residues (mod *n*) of one googol, starting with mod 1, is as follows:

- 0, 0, 1, 0, 0, 4, 4, 0, 1, 0, 1, 4, 3, 4, 10, 0, 4, 10, 9, 0, 4, 12, 13, 16, 0, 16, 10, 4, 16, 10, 5, 0, 1, 4, 25, 28, 10, 28, 16, 0, 1, 4, 31, 12, 10, 36, 27, 16, 11, 0, ... (sequence A066298 in the OEIS)

This sequence is the same as that of the residues (mod n) of a googolplex up until the 17th position.

Widespread sounding of the word occurs through the name of the company Google, with the name "Google" being an accidental misspelling of "googol" by the company's founders,^{[6]} which was picked to signify that the search engine was intended to provide large quantities of information.^{[7]} In 2004, family members of Kasner, who had inherited the right to his book, were considering suing Google for their use of the term googol;^{[8]} however, no suit was ever filed.

Since October 2009, Google has been assigning domain names to its servers under the domain "1e100.net", the scientific notation for 1 googol, in order to provide a single domain to identify servers across the Google network.^{[9]}^{[10]}

The word is notable for being the subject of the £1 million question in a 2001 episode of the British quiz show *Who Wants to Be a Millionaire?*, when contestant Charles Ingram cheated his way through the show with the help of a confederate in the studio audience.^{[11]}

**^**Bialik, Carl (June 14, 2004). "There Could Be No Google Without Edward Kasner".*The Wall Street Journal Online*. Archived from the original on November 30, 2016. (retrieved March 17, 2015)**^**Kasner, Edward; Newman, James R. (1940).*Mathematics and the Imagination*. Simon and Schuster, New York. ISBN 0-486-41703-4. Archived from the original on 2014-07-03. The relevant passage about the googol and googolplex, attributing both of these names to Kasner's nine-year-old nephew, is available in James R. Newman, ed. (2000) [1956].*The world of mathematics, volume 3*. Mineola, New York: Dover Publications. pp. 2007–2010. ISBN 978-0-486-41151-4.CS1 maint: ref=harv (link)**^**McPherson, Kristine (2006). Elert, Glenn (ed.). "Mass of the universe".*The Physics Factbook*. Retrieved 2019-08-24.**^**Sagan, Carl (1981).*Cosmos*. Book Club Associates. pp. 220–221.**^**Particle emission rates from a black hole: Massless particles from an uncharged, nonrotating hole, Don N. Page,*Physical Review D***13**(1976), pp. 198–206. doi:10.1103/PhysRevD.13.198. See in particular equation (27).**^**Koller, David (January 2004). "Origin of the name "Google"". Stanford University. Archived from the original on July 4, 2012. Retrieved July 4, 2012.**^**"Google! Beta website". Google, Inc. Archived from the original on February 21, 1999. Retrieved October 12, 2010.**^**"Have your Google people talk to my `googol' people". Archived from the original on 2014-09-04.**^**Cade Metz (8 February 2010). "Google doppelgänger casts riddle over interwebs". The Register. Archived from the original on 3 March 2016. Retrieved 30 December 2015.**^**"What is 1e100.net?". Google. Archived from the original on 9 January 2016. Retrieved 30 December 2015.**^**Falk, Quentin; Falk, Ben (2005), "A Code and a Cough: Who Wants to Be a Millionaire? (1998–)",*Television's Strangest Moments: Extraordinary But True Tales from the History of Television*, Franz Steiner Verlag, pp. 245–246, ISBN 9781861058744.

**^**≈1.1979×10^{100}

- Weisstein, Eric W. "Googol".
*MathWorld*. - googol at PlanetMath.org.
- Padilla, Tony; Symonds, Ria. "Googol and Googolplex".
*Numberphile*. Brady Haran. Archived from the original on 2014-03-29. Retrieved 2013-04-06.

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