Large Numbers
The earlier parts of this article are very well summarised
by Adam Townsend in the wonderful article in UCL's
This page begins with million, billion, etc., proceeds through Googolplex and Skewes' numbers (organised into "classes" based on the height of the powertower involved), then moves on through "tetration", the Moser and the "GrahamRothschild number", on to lesserknown hierarchies of recursive functions, the theory of computation, transfinite numbers and infinities. If it's a number and it's large, it's probably here.
Contents
Class 1 Numbers (like 100)
Class 3 Numbers (like googolplex)
The Quality of Uncomputably Larger
Inventing New Operators and Functions
Why Function Hierarchies Require a Transfinite Ordinal Index
Why There are Competing Function Hierarchies
Beyond Exponents: hyper4 (Tetration)
Hyperfactorial and Superfactorial
The "Generalised Hyper" Function
Bowers' Array Notation (3element Subset)
A Partial Ordering for Knuth UpArrows
A Partial Ordering for the Hyper Function
SteinhausMoserAckermann Notation/Functions
The various "Graham's number"s :
The "GrahamRothschild Number"
Friedman Block Subsequence Length
Conway's Chained Arrow Notation
A Partial Ordering for short Conway chains
More Bowers Constructions :
Bowers' Array Notation (4element Subset)
Bowers Arrays with 5 or More Elements
Generalised Invention of Recursive Functions
The LinRado/Goucher/Rayo/Wojowu Method
Declarative Computation and Combinatory Logic
Computation by Formal Logic and Set Theory
Direct Declaration of the Existence of a Number
Doing Maths in FirstOrderLogic and Set Theory
Transfinite and Infinite Numbers
The First Cardinal Infinity: AlephNull
The Ordinal "Countable" Infinities
All Ordinals Countable by Reordering
The Power Sets of the Continuum
Bibliography and other References
Author's Introduction
Large numbers have interested me almost all my life.
This page covers all the huge numbers I have seen discussed in books and web pages, and it actually does so in numerical order, as near as I can tell (see the uncomparable and superclass 5 discussions).
One important thing to notice is that all discussions like this ultimately lead to difficult and unsolved problems in the theory of algorithms and computation. This page ends with Turing machines just before crossing over to the transfinite numbers. If you want to learn something about the theory of algorithms and computation, get two or more fairly knowledgeable people to compete at describing the highest number they can, and then stand back!. One such competition (detailed in a footnote) took only a few days to move beyond the range of everything discussed in the first twothirds of this webpage, and then spent another few years discussing formal proofs.
This page is meant to counteract the forces of Munafo's Laws of Mathematics. If you see room for improvement, let me know!
Classes
First of all, I'm going to define what I call "classes" of numbers. This is a version of the "levels of perceptual realities" in an article On Number Numbness by Douglas Hofstadter [41], [43]. I have set arbitrary breakpoints (6, 10^{6}, etc.) that are based on wellresearched results regarding how perception and cognition handle numbers and quantities.
[...]If [the] numbers [have] millions or billions of digits, the numerals themselves (the colossal strings of digits) would cease to be visualizable, and your perceptual reality would be forced to take another leap upward in abstraction — to the number that counts the digits in the number that counts the digits in the number that counts the objects concerned.[...]
It is a powerful and basic concept but usually goes unsaid. I think you'll agree that something like this makes sense (though perhaps you might choose your own arbitrary points of separation between the subitisable and the quotidian). In addition to these distinctions that relate to perception and cognition, the categories correspond to computational abilities, such as whether it is possible for your computer to store enough digits to resolve the effect of adding 1, whether it is possible to resolve the effect of multiplying by 2, and so on. Almost all numbers that are easy to make simple statements about (such as which of two numbers is larger) can be put into the class system.
All numbers that anyone ever has to deal with in any practical application (unless you count abstract mathematics and nerdy oneupmanship contests as practical :) are members of one of the first four classes. Two, a hundred, googol, and googolplex are examples from classes 0 through 3, respectively.
Class0 Numbers
Class0 numbers are those that are small enough to have an immediate intuitive or perceptual impact. Perceiving such a number is called subitising, and for most purposes the limit has been shown to be somewhere from 5 to 9 (see Kaufman [32] and Miller [33]). I'll be a bit conservative here and place the limit at six. So, the numbers 1 through 6 are class 0.
Experiments with animals, when properly set up and conducted, demonstrate ability to identify numbers of objects and exhibit different behavior based on whether the number of objects is equal to some specific value — for example, pressing a lever only when five objects are present. Such experiments also show that the animal's ability to perform the feat falls off sharply between 4 and 8: the task can almost always be performed reliably when the number is 4, and can seldom be performed reliably when the number is 8 (with intermediate results inbetween).
In the days of anthropological research by scientists from Europe who were encountering other cultures for the first time, it was discovered in some cases that a group of people had words for a few of the smaller numbers (say, up to three) but not beyond that. Due to a misunderstanding of the difference between having a word for a number and being able to perceive and understand precise quantities, this led to some myths that the people in such cultures couldn't count any higher than three or some other small number. Such a belief or myth reflects the basic truth that there is some additional abstraction or understanding involved when an amount is greater than what is subitizable.
One way to see this phenomenon for yourself is to use flash cards (or a computer program set up to simulate flash cards) that present pictures of objects that can be counted and placed in random arrangements — but look at the picture only long enough to see it, and not long enough to do any type of counting. It is not allowed to use regular arrangements like grids, or any other distinguishing attributes such as multiple colours or shapes. After the picture is hidden, try to answer how many objects there were. You then try to count the number of objects in your mental image of the picture you've just seen. If the number of objects is a class 0 number, you'll usually be able to give the right answer. As you increase the numbers of objects, your counts will be less and less likely to be correct. Obviously, this gives a rather fuzzy definition of "class 0", but the value you get will almost always be consistent with Miller's result of "seven plus or minus two". [33]
Class1 Numbers
Class1 numbers are those that are small enough to be perceived as a bunch of objects seen directly by the human eye. What I mean by "seen directly" is that it is possible to see the number as a set of separate, distinct objects in a single scene (no time limit, but the observer and the objects cannot move). 100 is a class1 number because it is possible to see 100 objects (goats for example) in a single scene. The limit for class1 numbers will vary depending on the use of colours, etc. and the quality of one's vision, but for black dots on white background most people would probably be able to see around a million, 1,000,000 or 10^{6}. You can just barely put 1,000,000 dots on a large piece of paper and stand at a distance such that you can perceive each individual dot as a distinct dot, and at the same time be within viewing distance of the other 999,999 dots. (I have actually done this, just for fun!) As with Class0 the definition is fuzzy, some people have better vision and could manage 10,000,000 dots or even more.
The earliest conscious communication of numbers between humans was probably limited to class0 and very low class1 numbers, because of simple physical methods of counting (like fingers and toes). The first written number systems consisted of tally marks and extended into the class1 range. (Methods involving objects or symbols that each count for 5, 10 or larger values, came later, see below.)
Class1 numbers include all of the quotidian (everyday) quantities bigger than the subitizable, and because they occur so often, people can comfortably handle or perceive them due to experience and familiarity. For values in class 1, it is easy to distinguish the magnitude of the value just by looking at it. Most people have realised that, if they walk into a room with 85 people, although they can't tell it's exactly 85, they know right away it's somewhere around 75 to 100. No thought or calculation is necessary. This is an immediate perception of magnitude, and the ability extends to numbers up into the thousands and tens of thousands, with less percentage accuracy as the amounts increase. A person in a stadium with 10,000 people will have a fuzzier magnitude perception (they might guess anywhere from 3,000 to 30,000). By the time we get to numbers like 10^{8} (the number of blades of grass in an acre) a person is probably about as likely to believe "10 million" (10^{7}) as "a trillion" (10^{12}) unless they take the time to do some calculations (Fermi estimation would be adequate).
Class1 numbers also include most types of things that people aggregate or count with the passage of time. If you have kept count of how many times you have done something (e.g. jogging) or the number of things in a collection (e.g. stamps) it probably numbers in the class 1 range. The actual act of counting usually wears out before exceeding class 1, partly because of the difficulty of accurately remembering the digits. (Supposing you need to remember the number from one day to the next — no written or other aids, keeping count of the number of days you have jogged this year is much easier than keeping count of how many steps you have taken this year — once that number gets into 6 or 7 digits mistakes are very likely for most people).
Symbolic representations of numbers soon became common. The earlier systems were just tallymarks with lots of different symbols, like one symbol to represent 1's and another to represent 10's, etc. Roman numerals are the mostused example of this. Often, different types of physical objects (like round and flat stones) were used for counting. Many examples are described in [47]. With symbolic systems it became easy for people to express, write, and do arithmetic with numbers throughout the class1 range. Such representation systems usually reached their limit right around 1,000,000 for the same reasons that class0 perceptive abilities are limited to 6: it is difficult to keep track of lots of different types of symbols/objects at once, and 5 or 6 types of symbols/objects is a practical limit — but the limit also existed because there was little need to deal with larger numbers. As in modern times, larger units were used when smaller ones were inconvenient — one does need to worry about the last few centimetres when considering a distance of 123.4 km.
Class2 Numbers
Class2 numbers are those that can be represented in exact form using decimal placevalue notation (or another small integer base, like base 2, 16 or 60). Typically this depends on how the digits are recorded and what you need to do with them. Since I used 6 as the upper limit of class 0, and 10^{6} = 1000000 for the upper limit of class 1, I'll just continue the pattern and say that the class2 numbers go from 10^{6} to about 10^{1000000}.
Placevalue notation was popularised in the Arabic culture (but came from India, and perhaps from China before that, again see [47]). It opened up the range of class2 numbers to anyone who wanted to use them. It was no longer necessary to come up with new symbols for each successive power of 10. Generalizations in arithmetic rules were obvious: adding 2000+7000 was not only analogous to adding 2+7, it was essentially the same thing. Handling huge numbers became easy. To make an exact calculation about thousands of objects, only a handful of objects (the digits) need to be manipulated.
Googol is a class2 number, as are the various large prime numbers used in cryptography, all of the known Perfect numbers (until 1997!), the Fermat numbers with known factorization, etc. All of the large physical constants like 6.02×10^{23} (Avogadro's number) and 10^{80} (the number of protons in the universe) are class2. So are most of the numbers with names ending in illion, like vigintillion (10^{63}), centillion (10^{303}), and on up to the somewhat contrived millimillillion (10^{3000003}) (which, by my admittedly arbitrary decision, is a bit beyond the class2 range).
The Big Number Names of Nicolas Chuquet
The word million comes from around 1270^{2}, and entered the English language around 1370^{6}. The names billion, trillion, and so on up to nonillion, plus the general idea of continuing with Latinderived prefixes all first appear in the late 15^{th} century, in writing by Nicolas Chuquet, a French mathematician living in Lyon from 1480 until his death in 1488. (There were also the longer forms bymillion and trimillion used as early as 1475 by Jehan Adam, but these never caught on). Follow this link for more details: Origins of the Chuquet number names.
Peletier's Proposal and the Short Scale
In 1549 Jacques Peletier repeated the suggestion that billion should be one million million = 10^{12}, and trillion for 10^{18} and so on. He also introduced^{1},^{2} the use of milliart, billiart and so on to represent the skippedover powers of 1000, like 10^{9} and 10^{15}.
The long scale is Chuquet's original system, and has digits grouped 6 at a time, thus trillion is a million times larger than billion. This is the "billion=10^{12} system". Peletier's names for 10^{(6N+3)} (in the English spelling, milliard=10^{9}, billiard=10^{15}, etc.) are compatible with this system.
The use of numbernames during the following few centuries eventually led to widespread usage of billion to mean 10^{9}, trillion for 10^{12}, and similar redefinitions of the higher names. These definitions are the short scale or "billion=10^{9} system". Follow this link for more on the history of short vs. long scale. Here is a related video by Numberphile: How big is a billion?.
Zillions: BigNumber Words as a Hyperbolic Adjective
While the confusion between short and long scale was becoming wellestablished, the bignumber words ending in illion were also becoming popular for the purpose of espressing an excessively or unimaginably large, or even infinite, quantity. This is a type of usage that was already common for hundreds, thousands, myriads and millions. For example, OED's [44] HUNDRED heading 2 a. begins: "Often used indefinitely or hyperbolically for a large number: cf. thousand. (With various constructions, as in [heading] I.)", and then gives nine quotations dating from 1300 AD to 1885. In the following table I show the first documented use of each numbername in both the literal sense and in this "superlative" sense.
(It should be noted that zillion more generally can refer to far larger things. For example, Howard DeLong[36] used the term "zillion" to refer to an iterated Ackermann function of some other really large number c_{1}.[51]
Standard Accepted Names and SI Prefixes
This table shows all positive powers of ten that have authoritatively accepted names in English (by [44]) up to Chuquet's highest name nonillion. The numeric values here follow the billion=10^{9} system ("short scale"). I am also including a few other nonpowers of 10 that have names in English, but leaving out many base20 constructions and other names less than 100, about which you can read plenty in [47]. I include all former and current official SI prefixes because they are quasi"words" that have a purely numerical meaning. The dates of first literal and superlative usage are largely from OED [44] but are augmented as indicated in the footnotes.
The Standard Names and SI Prefixes
N  N in Latin ^{3},^{18}  10^{3N+3}  name for 10^{3N+3}  first literal usage [44]  first superlative usage [44]  SI prefix(es)^{20} 
10^{1}  ten  deca or deka (da,dk)  
10^{2}  hundred  950 AD  1300  hecto (h)  
10×12  great hundred  1533  
12^{2}  gross  1411  
0  10^{3}  thousand  971 AD  1000  kilo (k)  
2^{10}  1024  kibi (ki)  
12^{3}  great gross  1640  
10^{4}  myriad  1555  1555  myria (my)  
1  unus  10^{6}  million  1370  1362  Mega (M) 
2^{20}  1048576  Mebi (Mi)  
2  duo  10^{9}  great million, milliard, billion  1625, 1793, 1690^{21}  ?, 1823^{22}, ?  kilomega, Giga (G) 
2^{30}  1073741824  Gibi (Gi)  
3  tres  10^{12}  trillion  1690^{21}  1847^{23}  megamega, Tera (T) 
2^{40}  1099511627776  Tebi (Ti)  
4  quatuor  10^{15}  quadrillion  1674^{21}  1855^{23}  Peta (P) 
2^{50}  1125899906842624  Pebi (Pi)  
5  quinque  10^{18}  quintillion  1674^{21}  1855^{23}  Exa (E) 
2^{60}  1152921504606846976  Exbi (Ei)  
6  sex  10^{21}  sextillion  1690^{21}  1855^{23}  Zetta (Z) 
2^{70}  1180591620717411303424  Zebi (Zi)  
7  septem  10^{24}  septillion  1690^{21}  ?  Yotta or Yotto (Y) 
2^{80}  1208925819614629174706176  Yobi (Yi)  
8  octo  10^{27}  octillion  1690^{21}  1855^{23}  
9  novem  10^{30}  nonillion  1690^{21}  ? 
Chuquet left it to others to work out the details of extending the names beyond nonillion. Although there is much discrepancy between the actual numbernames in Latin and the illion names Chuquet listed, it was nevertheless understood that Latin numbernames were to be used to extend the names as needed. Using Latin for prefixes goes smoothly as far as vigintillion. The following names are found in many dictionaries^{19}; vigintillion and centillion are a little more common than the others. Some popular nondictionary sources have made reference to millillion and millimillillion (mostly due to Henkle/Brooks, and Borgmann [35]).
Larger Standard Names Beyond Chuquet's Nonillion
N  N in Latin ^{3},^{18}  10^{3N+3}  name for 10^{3N+3} 
10  decem  10^{33}  decillion 
11  undecim  10^{36}  undecillion 
12  duodecim  10^{39}  duodecillion 
13  tredecim  10^{42}  tredecillion 
14  quattuordecim  10^{45}  quattuordecillion 
15  quindecim  10^{48}  quindecillion, quinquadecillion 
16  se(x)decim  10^{51}  sexdecillion, sedecillion 
17  septemdecim  10^{54}  septendecillion 
18  duodeviginti^{24}  10^{57}  octodecillion 
19  undeviginti^{24}  10^{60}  novemdecillion, novendecillion 
20  viginti  10^{63}  vigintillion 
10^{100}  "googol" = ten duotrigintillion  
100  centum  10^{303}  centillion 
1000  mille  10^{3003}  millillion 
1000000  decies centena milia  10^{3000003}  millimillillion 
10^{10100}  "googolplex" 
The ConwayWechsler System
Chuquet's names are notable for:
 being wellresearched,
 being faithful to Latin within limits of utility,
 retaining the meaning of existing widelyused names,
 being proposed by a respected wellknown mathematician
The Henkle/Brooks names of the late 19^{th} century fall short of that mark on one or two counts.
Today it is useful to consider systems proposed by those other than "a respected wellknown mathematician". The vast majority of huge numbers in use by the general population are in incremental games and similar recreations. Most of the work in extending the frontiers of practical computation with large numbers has been done in software libraries that facilitate such games. Therefore, we should not aspire to the four advantages of Chuquet I just listed, but instead something more like this:
In order for a system of words (names) to be useful by a set of people (perhaps sharing a specific field of application, or having cultural links such as a shared language), a system of words/names should do well by the following measures:
 The words/names meet a need, i.e. they refer to things that need to be discussed, and do not already have names fitting the other criteria listed here. (for example, most of the "adhoc Googolisms", which name numbers that are too long to write out, name things that are so big they are never discussed outside the articles written by their own creators.)
 The words/names have etymological structure that aids in learning or remembering their meaning. (for example, the use of Greek number roots in the Knuth yllion System.)
 The words/names fit a pattern that facilitates extension or interpolation when needed (for example, the common use of illion to mean "power of 1000" and plex to mean "10 to the power of". The "adhoc Googolisms" mentioned earlier give no way to create compatible names for arbitrary values; incremental games instead use symbolic expressions based on function hierarchies.)
 All the little decisions have been considered carefully enough to find the "best" option, so that the choice made is not arbitary (for example, the choice of "zepto" over "septo" in the SI Prefixes, or any similar decision motivated by making something that works in multiple languages)
The system is based on the short scale (billion=10^{9}) but the names could easily be used in a long scale system. A number name is built out of pieces representing powers of 10^{3}, 10^{30} and 10^{300} as shown by this table:
1's  10's  100's  
0       
1  un  ^{n} deci  ^{nx} centi 
2  duo  ^{ms} viginti  ^{n} ducenti 
3  tre ^{*}  ^{ns} triginta  ^{ns} trecenti 
4  quattuor  ^{ns} quadraginta  ^{ns} quadringenti 
5  quin  ^{ns} quinquaginta  ^{ns} quingenti 
6  se ^{sx}  ^{n} sexaginta  ^{n} sescenti 
7  septe ^{mn}  ^{n} septuaginta  ^{n} septingenti 
8  octo  ^{mx} octoginta  ^{mx} octingenti 
9  nove ^{mn}  nonaginta  nongenti 
The rules are:
 Take the power of 10 you're naming and subtract 3.
 Divide by 3. If the remainder is 0, 1 or 2, put one, ten or one hundred at the beginning of your name (respectively).
 For a quotient less than 10, use the standard names thousand, million, billion and so on through nonillion. Otherwise:
 Break the quotient up into 1's, 10's and 100's. Find the appropriate name segments for each piece in the table. (NOTE: The original ConwayWechsler system specifies quinqua for 5, and Miakinen suggests quin.)
 String the segments together, inserting an extra letter if the letter shown as a superscript at the end of one segment matches a letter in parentheses at the beginning of the next. For example: septe^{mn} + ^{ms}viginti = septemviginti because both superscripts contain an m; but se^{sx} + ^{n}ducenti = seducenti with no added letter because there is no matching letter in "^{sx}" and "{n}". Another example: se^{sx} + ^{ns}quingenti = sesquingenti.
 For the special case of tre, the letter s should be inserted if the following part is marked with either an s or an x.
 Remove a final vowel, if any.
 Add illion at the end. You're done.
The 1's column in combination with deci in the 10's column seem designed to replicate the names in established usage (shown above, here and here), with three differences. Miakinen comments ^{4} on these, which concern 15, 16, and 19:

I agree with Miakinen and thus I have put quin in row 5 of the 1's column above, instead of quinqua.
Going beyond vigintillion into territory newly covered by ConwayWechsler, some nearambiguities arise. For example 10^{261} is sexoctogintillion and 10^{2421} is sexoctingentillion. Then there's 10^{309} = duocentillion while 10^{603} = ducentillion; and similarly 10^{312} = trescentillion while 10^{903} = trecentillion.
This system seems to have been widely adopted, based on the diversity of results I find with online searches in 2022 (including a lot of videos related to incremental games and whoknowswhat else). It seems that the subtleties of spelling (and probably pronunciation) haven't been too much of a concern, as I find more spelling errors that are due to other causes.
The ConwayWechsler system extends to arbitrarily high values. After setting out the rules above, the authors continue^{7}:
With Allan Wechsler we propose to extend this system indefinitely by combining these according to the convention that "XilliYilliZillion" (say) denotes the (1000000X + 1000Y + Z)th zillion, using "nillion" for the zeroth "zillion" when this is needed as a placeholder. So for example the millionandthird zillion is a "millinillitrillion."
As their example shows, the beginning parts of the standard names such as million and trillion are used for the "1" and "003" parts (respectively) of the number 1,000,003, with the placeholder "nilli" for the central "000" portion. This is the "1,000,003^{rd} zillion", which is 10^{3×1000003+3}=10^{3000012}. In general, when naming 10^{3N+3}, the rules above are to be used for each group of 3 digits in the number N.
For another example, consider 10^{19683}: this is 10^{3×6560+3}, so N=6560. That breaks up into a "6" part (the standard sextillion) and a "560" part (sexagintaquingentillion by the above table and rules); these are combined to form sextillisexagintaquingentillion which is the full ConwayWechsler name for 10^{19683}.
Their name for googolplex is ten trillitrestrigintatrecentilli....trestrigintatrecentilliduotrigintatrecentillion; with the "...." replaced by 30 additional repetitions of "trestrigintatrecentilli". This name is two words and 3+766 letters long.
See more examples of ConwayWechsler number names here.
There have also been numerous personal or adhoc Chuquet extensions, follow that link for more.
A Practical Alternative
If the above tables seem a bit much to deal with, here is my modest proposal for a simpler naming system:
 Learn a few of the smaller powers of 1000.
 Beyond that, use "Ten to the power of..." followed by the appropriate class 1 number.
. . . Forward to page 2 . . . Last page (page 11)
Japanese readers should see: 巨大数論 (from @kyodaisuu on Twitter)
If you like this you might also enjoy my numbers page.
This page was written in the "embarrassingly readable" markup language RHTF, and some sections were last updated on 2024 Mar 12. s.30