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SI Prefixes
The original SI (systeme international, or "Metric" system) in 1793 had only the prefixes kilo, hecto, deca, deci, centi, and milli. In 1795 myria was added but later became deprecated. mega dates from the late 1800's and was officially adopted in France in 1919. During the 1900's kilomega and megamega were used but it was eventually decided these needed their own prefixes^{3}; giga, nano and tera, pico were adopted in 1960, femto and atto in 1964, peta and exa in 1975, and zetta, zepto and yotta, yocto in 1991. These extensions have been added mainly for the convenience of scientists. For example, in 1993 some researchers had to refer to units of 10^{21} volts but they didn't yet know about the prefix zepto so they called it "milliattovolt". There have always been fields where very small or very large values are expressed simply as big exponents of 10, or where a fieldspecific and somewhat arbitrary unit such as the parsec or electronvolt is used. The standard unit of atomic mass (1/12 the mass of a Carbon atom, or roughly the mass of a proton or a neutron) is 1.66×10^{27} kg or 1.66 yg (1.66 yoctograms). Quasars have been discovered that are about 125 yottameters away. When volumes or weights are involved the units are even more often found to be insufficient — the Earth weighs about 6000 Yg (6000 yottagrams), and the mass of an electron is about 0.00091 yg (yoctograms). By comparison, the diameter of the Earth and of an atom (both onedimensional measurements) are both easily handled with the older kilo and pico prefixes.
The following "SI prefixes" are deprecated or obsolete: myria, kilomega, and megamega.
The official SI prefix names "peta" and "exa" are probably derived from "pente" and "hexa" (five and six in Greek)^{3}, however, the official BIPM (Bureau International des Poids at Mesures) website does not give an explanation.
"Zetta" and "yotta" are derived from "septo" and "octo", which are quasi number names. Quoting BIPM:^{13}
The names zepto and zetta are derived from septo suggesting the number seven (the seventh power of 10^{3}) and the letter "z" is substituted for the letter "s" to avoid the duplicate use of the letter "s" as a symbol. The names yocto and yotta are derived from octo, suggesting the number eight (the eighth power of 10^{3}); the letter "y" is added to avoid the use of the letter "o" as a symbol because it may be confused with the number zero.
If BIPM decides to adopt further prefixes for 10^{27} and 10^{30} and their reciprocals 10^{27} and 10^{30}, they will probably adopt something vaguely resembling names for nine and ten for a similar reason — perhaps something like novetta, novemo, decetta and decemo. If so they would almost certainly be assigned twoletter abbreviations such as "No", "De", "no" and "de" because N, n and d are already used for other prefixes.
Joke, Hoax, and Sincere (but AdHoc) SI Prefix Proposals
The following prefixes have all been exposed as jokes or hoaxes: bronto, cuppa, dea, ento, fito, harpo, hepa, lotta, lotto, nea, otta, revo, syto, tredo, una, xera, zeppo, and zuppa^{3},^{27},^{28},^{29},^{33},^{34}. Several of these were perpetuated by Internet rumors (compare two posts by Alex LopezOrtiz ^{4},^{11}), and many go back before widespread use of the Internet^{12}.
One of the earliest examples was apparently a reaction to the sillysounding and real prefixes yocto and zepto. In 1993, as a joke that was reportedly well received on USENET, Morgan Burke^{27} proposed harpo for 10^{27} and groucho for 10^{30} (and therefore harpi for 10^{27} and grouchi for 10^{30})^{29}.
In addition, the following are simply bogus adhoc personal ideas: luma, lunto, mikto, minga, nekto, nena, ocha, otro, pekro, pepta, quekto, quexa, rimto, rinta, sorta, sotro, treda, trekto, uda, udeka, udeko, unto, vendeka, vendeko, vunda, vunkto, weka, weko, wekta, wekto, xenno, xenta, xona, and xonto^{10}.
Oxford professor Jeff K. Aronson has suggested extending beyond zetta, zepto and yotta, yocto with xenta, xenno, wekta, weko, vendeka, vendeko, udeka, udeko based on the idea that the 'Z' and 'Y' prefixes would continue backwards through the English or modern Latin alphabet.
An essentially equivalent proposal was made by Paul Shuch in a letter to Science News ^{35}, suggesting acto=10^{96}, atta=10^{96}, etc. through wocto=10^{30}, wotta=10^{30}, xocto=10^{27}, and xotta=10^{27}.
Using a similar idea, Jim Blowers^{10} says:
The pattern here is that we go backwards from the beginning of the alphabet [shouldn't this be "end of the alphabet"? ed], starting with z and y, and we follow it up with an alteration of the Greek or Latin for the next number. According to this pattern, the next ending ["prefix" ed] should be xona, since x comes before y in the alphabet, and 9 is noni in Latin. Similarly, 10^{30} should be weka, since w precedes x and 10 is deka in Greek.
He goes on to list a large number of prefixes starting with Xona, Weka, Vunda, Uda, Treda, Sorta, ... Oneletter abbreviations are used if unambiguous, otherwise another letter is added, e.g. TD for the Treda prefix. He goes as far as 10^{63} using an L prefix, based on the 26letter "Latin" alphabet used in several European languages including English, although the original classical Latin language had no U or W.
Any of these might be (intentionally of mistakenly) used by others who are sincere, but unaware that the prefix they are using is unofficial, adhoc or worse. For example, one reader wrote to me informing me of the usage of Xera by a Dr. Laurent Alexandre.
Sources
Here is a collection of URLs that are related to the above topics, but which I did not actually use as sources. Most of these are from the beginning of my work on this page (around 1999 or 2000). These pages concern names of large numbers, SI units, and similar things.
(Sources:
Borislav Manolov, Names of large and small numbers, web page.
InterTran EnglishLatin Translator, via Stars21.
http://www30.brinkster.com/manfear/office/large.html (Also gives names in German and proposes names based on Greek)
http://g42.org/MiscInfo/numbers.html (Much of the same info as on the previous page)
http://www.unc.edu/%7Erowlett/units/large.html (Much of the same info as on the previous page)
http://mathforum.org/library/drmath/view/59155.html (An introduction for kids)
http://www.grammarstation.com/KnowYourMath/numbers_symbols.html (An introduction for kids)
http://www.ex.ac.uk/cimt/dictunit/notesp.htm (Described the SI prefixes for powers of 1024, but now offline)
http://mathworld.wolfram.com/LargeNumber.html
http://journals.iranscience.net:800/www.newscientist.com/www.newscientist.com/lastword/article.jsp@id=lw77 (comments on uses of zetta and yotta)
http://www.lewrockwell.com/orig/kinsella6.html (introduction to the SI units)
http://www.plexos.com/256_bit_CPUs_should_be_enough.htm (xona)
http://jimvb.home.mindspring.com/unitsystem.htm (xona)
http://www.omniglot.com/writing/latin.htm (Latin alphabet)
http://www.freezoneearth.org/Prometheus04/otThree/preot3/bignumbers.htm
Wikipedia, List of numbers (Another version that goes up to 10^{180}) )
Adhoc Googolisms
Recently there has emerged a smaller but more dedicated community of people who invent many, many names for specific large numbers. These names are similar in spirit to the Adhoc Chuquet names; in particular their creators promote the names as if they wish them to become part of the language.
An early and wellknown creator is Jonathan Bowers, who makes up a lot of names for examples of every successive fastgrowing function in his large numbers system.
myrillion=10^{30003} micrillion=10^{3000003} (same as Henkle's milli_millillion), killillion=10^{3×103000+3} megillion=10^{3×103000000+3} gigillion=10^{3×103000000000+3} tedakillion=10^{3×103×1042+3} (having run out of SI prefixes) ... giggol = 10^{④}100 (described here) giggolplex = 10^{④}(10^{④}100) trisept = 7^{(7)}7 tridecal = 10^{(10)}10 boogol = 10^{(100)}10 ...
and a ton of names for numbers that are easy to express in his Array Notation, "extended" erray notation, "exploding" arrays, and so on.
Some time after Bowers the Googolgy wiki began, and eventually gained a very large membership and thousands of pages for specific names. Examples:
novopastillion = 10^{(3×103×1027×1021+3×103×1015×1012+3)} named by "Trakaplex")(334).
goomolplexiduex = 10↑↑10↑10↑1000 named by "Username5243"(355).
forcal = 3↑↑↑↑3, the first step in the construction of Graham's number, named by Aarex Tiaokhiao(958).
egisitriplextron = M(M(M(M(10,3),3),3),3) in Aarex's "HyperMoser notation" (which is equivalent to the SteinhausMoser notation), also named by Aarex Tiaokhiao.
gongulusquadraplex = {10,10 (gongulustriplex) 2} in Jonathan Bowers' "Exploding Array" notation, named by Jonathan Bowers(363).
truchainpribolplex = s(3,3,3,2,4) in "Hyp cos"(597)'s "strong array notation", named by "Hyp cos"(597).
Empirititaniprimol = #{1:1:1}((10))*100 in "SuperJedi224"'s "HyperExploding PoundStar Notation", named by "SuperJedi224"(388).
*godgralgathtothol = E100#^(#^#^##^##)100 in Sbiis Saibian's "CascadingE notation", named by Sbiis Saibian(6873).
bigrand giaquaxul = (...((200![200,200,200,200])![200,200,200,200])![200,200,200,200]...)![200,200,200,200] in Lawrence Hollom's "Hyperfactorial array notation", named by Lawrence Hollom(548).
trimixommwil = f_{ψ0(Ωψ0(Ωψ0(Ω)))}(10) in the Fastgrowing hierarchy, named by Denis Maksudov(676).
In nearly all cases the number names come from the person who defined the notation that is used to define the number. This typically happens because the notation systems require extensive explanation with clarifying examples, and the names help make the examples less awkward to present. In most cases, there are patterns used in the names (such as the incorporation of SI prefix syllables), and this makes many of the names only minimally different from each other. Sbiis Saibian is notable for having named thousands of numbers, most of them with a single word (perhaps hyphenated).
Huge Numbers in Idle/Clicker Games
There has emerged a class of games, called "Idle" or "Clicker" games, usually played in a browser. A wellknown early example is "Cookie Clicker" by Orteil; another with which I am fairly familiar is Sandcastle Builder by Eternal Density.
These games motivate the player mainly to make some quantity ever larger. Often there is a "score" that continues to grow throughout the game, slowly at first and ever more quickly. Some aspects of human psychology have the effect of making a fixed increase seem smaller when the thing being increased is large. This means that some kind of accelerating growth (such as exponential) is typical of these games. Because of the common property of having gradually increasing values, attained by an endless sequence of small tasks, such games are categorised as "incremental games" (The "Clicker" type place more emphasis on constant interaction, while they "Idle" type place more emphasis on occasional interaction separated by significant gaps during which you can do something else.)
There is a limit to exponential growth in a browser game, and that is usually the IEEE double exponent range, about 10^{308}. To meet the needs of players, the game often bypasses this limit with custom number representations, computational algorithms, and display formats.
Following is a huge list of examples of numbers as they are given by the OmegaNum.js string conversion function, and the same numbers as displayed by the game "LNGI".

Gödel's undecidable sentence
The discipline of formal logic was described by Aristotle around 350 BC — although it was probably developed well before him. He described the syllogism, an inference of truth based on other established truths. For example:
if all integers are real numbers
and all primes are integers
then all primes are real numbers
Around 1850, George Boole refined formal logic by defining more precise symbols, axioms and rules, the result is called boolean algebra and propositional calculus.
Meanwhile, set theory was being developed by Georg Cantor and others.
Then Friedrich Ludwig Gottlob Frege began developing the predicate calculus. He applied existing formalism techniques to set theory and began developing a complete formalized system of arithmetic, symbolic logic, and set theory from basic axioms and inference rules. This work was just being published as Grundgesetze der Arithmetik vol. 2 when Bertrand Russell (a mathematician who was also wellknown as a writer) presented Frege with the following paradox:
Consider the class of all classes that are not a member of itself. Is this class a member of itself or not?
This paradox challenged Frege so completely that he had to withdraw his work because its foundation was flawed.
After toppling Frege's work, Bertrand Russell and Alfred North Whitehead began work on a similar and even more massive project, with corrections to the problems in Frege's approach and using some of the foundation axioms of Giuseppe Peano. Their goal was to make it possible to derive every true theorem in number theory by starting with a set of axioms and a set of inference rules, and methodically applying all the inference rules to the axioms and existing theorems to create new theorems. For examples, see the book Gödel, Escher Bach [45].
The technique of deriving all truth by an automatic process is appealing — it suggests the possibility of automation (e.g. by a mechanical or electronic computer) to eliminate human error in discovering proofs. However, from the start there was much doubt about whether it could ever be used to discover every truth in number theory (if it were possible, the technique would have completeness). For one thing, there was the issue of time and algorithmic complexity: the number of theorems that are provable in such a system is infinite, and all but a very very tiny fraction of those theorems are completely useless (true, but useless).
The goal of formalization was not questioned, and was continued across various fields of mathematics, e.g. by Hilbert.
Gödel finally showed that the Russell/Whitehead approach would not achieve completeness, in fact that no (sufficiently powerful) axiomatic system of number theory can prove all statements which are true in that system. He did this by showing how statements, expressions and theorems in a number theory system S could be used to encode its own symbols, axioms and inference rules. He then demonstrated that there exists a statement G in that system which asserts "Statement G cannot be derived through the axioms and inference rules of formal system S.". If G is indeed inferrable, then it is false — and the formal system S is inconsistent. But if G cannot be inferred, then it is true, and exists as an example of a true statement that cannot be inferred, and therefore demonstrates that S is incomplete. Thus, all sufficiently powerful formal systems of number theory are either inconsistent or incomplete.
It is now generally agreed that this phenomenon of incompleteness is a property of all axiomatic systems.
Notes on Skewes Number
The Skewes Numbers concern the distribution of primes, specifically how many primes exist that are below a certain number. The Skewes numbers set an upper bound for the point at which the number of primes ends up being less than the approximation "li(x)". See here for a complete description of the problem.
The following table gives the number of primes less than each power of 10:
n  10^{n}  primes 
1  10  4 
2  100  25 
3  1,000  168 
4  10,000  1,229 
5  100,000  9,592 
6  1,000,000  78,498 
7  10,000,000  664,579 
8  100,000,000  5,761,455 
9  1,000,000,000  50,847,534 
10  10,000,000,000  455,052,511 
11  100,000,000,000  4,118,054,813 
12  1,000,000,000,000  37,607,912,018 
13  10,000,000,000,000  346,065,536,839 
14  100,000,000,000,000  3,204,941,750,802 
15  1,000,000,000,000,000  29,844,570,422,669 
16  10,000,000,000,000,000  279,238,341,033,925 
17  100,000,000,000,000,000  2,623,557,157,654,233 
18  1,000,000,000,000,000,000  24,739,954,287,740,860 
19  10,000,000,000,000,000,000  234,057,667,276,344,607 
20  100,000,000,000,000,000,000  2,220,819,602,560,918,840 
21  1,000,000,000,000,000,000,000  21,127,269,486,018,731,928 
22  10,000,000,000,000,000,000,000  201,467,286,689,315,906,290 
(source: Caldwell)
Beyond about n=12 (and slightly larger values as computers get faster) this table cannot be produced by the direct method of finding each prime and counting. There was sufficient interest in this that, as early as 1867, Kulik had completed a table of the smallest factor of every integer (and therefore, giving all the primes) up to slightly above 100,000,000!
Soon after Kulik's table, Meissel found an indirect way to count the exact number of primes up to far higher numbers. His method was simplified by Lehmer in 1959, then improved by Lagarias, Miller and Odlyzko in 1985, and then improved further by Deleglise and Rivat.
The method has been improved to such an extent that it is actually possible to derive values of pi(x) for really huge values of x like 10^{100} or 10^{1000}. In 2005 Patrick Demichel found the actual point at which the pi(x) vs. Li(x) crossover occurs, 1.397162914×10^{316}. .
Comparing the GrahamGardner Number to Chained Arrow Numbers
The following three numbers are listed in ascending order:
3→3→64→2
the GrahamGardner number
3→3→65→2.
First, note the functionbased definition of the GrahamGardner number:
gn(n) = { hy(3,6,3) for n = 1 { { hy(3, gn(n1)+2, 3) for n > 1 GrahamGardner = gn(64)And we will give another similar definition for a function we'll call c3(N):
c3(n) = { 27 for n = 1 { { hy(3, c3(n1), 3) for n > 1Here is the expansion process for 3→3→N→2:
3→3→1→2 = 27 = c3(1)
3→3→2→2 = 3→3→(3→3→1→2) = 3→3→c3(1) = hy(3,c3(1),3) = c3(2)
3→3→3→2 = 3→3→(3→3→2→2) = 3→3→c3(2) = hy(3,c3(2),3) = c3(3)
and in general,
3→3→N→2 = c3(N)
Now note that:
c3(1) << gn(1) << c3(2)
c3(2) = hy(3, c3(1), 3) << hy(3, gn(1)+2, 3) = gn(2) << c3(2)
and in general
c3(N) = hy(3, c3(N1), 3) << hy(3, gn(N1)+2, 3) = gn(N) << c3(N+1)
therefore,
c3(64) = 3→3→64→2 << gn(64) = GrahamGardner number << 3→3→65→2 = c3(65)
A reader asked me how 3→3→3→3 compares to these:
3→3→3→3
= 3→3→(3→3→2→3)→2
= 3→3→(3→3→(3→3→1→3)→2)→2
= 3→3→(3→3→27→2)→2
= 3→3→c3(27)→2
= c3(c3(27))
therefore 3→3→3→3 is much bigger than the GrahamGardner Number.
What Turing and Church Did Not Prove
Turing is often credited with having proven that there are limits to what can be computed by computers, including all conceivable designs of realworld computers. This actually depends a lot on what you mean by computer. Here are some types of computers that a Turing machine cannot emulate:
 Ideal analog computers. This is a computer that manipulates real numbers in the form of analog quantities (like voltages) rather than digits. In an "ideal" analog computer, the quantity being represented is represented exactly, without any error. An example is a circuit that calculates square roots: If you put 2.0 volts on the input wire, it produces 1.4142135... volts on the output.
 Actual analog computers: Any realworld analog computer is subject to various sources of error, including fundamental limits of physics such as the brownian motion of molecules, the quantization of electric charge, and the uncertainty principle (Planck limits).
 Quantum computers: A quantum computer (ideal or actual) exploits properties of quantum mechanics, including most especially the ability for a "particle" such as a photon to be in a state that is indeterminate until that particle interacts with another particle. The conditions of the interaction and the original conditions of the indeterminate state's creation then determine what is observed. It appears that such interactions can be used to perform a sort of massively parallel computation.
 Nondeterministic computers: A nondeterministic computer incorporates some type of phenomenon that is not predictable, in the sense that no amount of advance knowledge can completely predict what the result of a computation will be. Sometimes such phenomena are deliberately exploited, such as a random number generator device based on a Geiger counter (and deriving its randomness from the unpredictable timing of radioactive decay events)
Each of these has one or more properties that make Turing's argument inapplicable. Usually this is some form of unpredictability on a fundamental level. For the ideal analog computers, Turing's argument does not apply because of the cardinality of the reals It is known that Turing planned to create a limitstocomputability proof for such computers, but that he never did (I suspect it was not because such computers are actually without limit!)
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