There are a wide variety of large numbers which crop up in mathematics. Some are contrived, but some actually arise in proofs. Often, it is possible to prove existence theorems by deriving some potentially huge upper limit which is frequently greatly reduced in subsequent versions (e.g., Graham's Number, KolmogorovArnoldMoser Theorem, Mertens Conjecture, Skewes Number, Wang's Conjecture).
Large decimal numbers beginning with are named according to two mutually conflicting nomenclatures: the American system (in which the prefix stands for in ) and the British system (in which the prefix stands for in ). The following table gives the names assigned to various Powers of 10 (Woolf 1982).
American  British  Power of 10 
Million  Million  10 
Billion  Milliard  10 
Trillion  Billion  10 
Quadrillion  10 

Quintillion  Trillion  10 
Sextillion  10 

Septillion  Quadrillion  10 
Octillion  10 

Nonillion  Quintillion  10 
Decillion  10 

Undecillion  Sexillion  10 
Duodecillion  10 

Tredecillion  Septillion  10 
Quattuordecillion  10 

Quindecillion  Octillion  10 
Sexdecillion  10 

Septendecillion  Nonillion  10 
Octodecillion  10 

Novemdecillion  Decillion  10 
Vigintillion  10 

Undecillion  10 

Duodecillion  10 

Tredecillion  10 

Quattuordecillion  10 

Quindecillion  10 

Sexdecillion  10 

Septendecillion  10 

Octodecillion  10 

Novemdecillion  10 

Vigintillion  10 

Centillion  10 

Centillion  10 
See also 10, Ackermann Number, Arrow Notation, Billion, Circle Notation, Eddington Number, GFunction, Göbel's Sequence, Googol, Googolplex, Graham's Number, Hundred, Hyperfactorial, Jumping Champion, Law of Truly Large Numbers, Mega, Megistron, Million, Monster Group, Moser, nplex, Power Tower, Skewes Number, Small Number, SteinhausMoser Notation, Strong Law of Large Numbers, Superfactorial, Thousand, Weak Law of Large Numbers, Zillion
References
Conway, J. H. and Guy, R. K. The Book of Numbers. New York: SpringerVerlag, pp. 5962, 1996.
Crandall, R. E. ``The Challenge of Large Numbers.'' Sci. Amer. 276, 7479, Feb. 1997.
Davis, P. J. The Lore of Large Numbers. New York: Random House, 1961.
Knuth, D. E. ``Mathematics and Computer Science: Coping with Finiteness. Advances in Our Ability to Compute Are Bringing Us Substantially Closer to Ultimate Limitations.'' Science 194, 12351242, 1976.
Munafo, R. ``Large Numbers.'' http://home.earthlink.net/~mrob/largenum.
Spencer, J. ``Large Numbers and Unprovable Theorems.'' Amer. Math. Monthly 90, 669675, 1983.
Woolf, H. B. (Ed. in Chief). Webster's New Collegiate Dictionary. Springfield, MA: Merriam, p. 782, 1980.
© 19969 Eric W. Weisstein