The Ultimate Guide To What Comes After Septillion: 10 Gigantic Numbers That Dwarf The Universe
The immediate successor to septillion is octillion. This is the simplest and most direct answer to the question of what comes next in the sequence of large numbers, as of December 19, 2025. Septillion, a number so large it is rarely used outside of theoretical physics or astronomy, is defined as $10^{24}$ (a 1 followed by 24 zeros) in the widely accepted short scale system. The next step up, octillion, is precisely one thousand times larger, representing $10^{27}$ (a 1 followed by 27 zeros).
However, the journey into the world of colossal numbers is rarely straightforward. To truly understand the sequence, one must immediately confront the fundamental difference between the "short scale" and the "long scale" systems of numerical nomenclature. This distinction is crucial because the name "septillion" can represent two vastly different numerical values depending on which system you are using, making the entire sequence a potential source of confusion for the uninitiated.
The Immediate Successor: Octillion and the Latin Ladder
In the modern world, particularly in the United States, most English-speaking countries, and the fields of finance and science, the short scale is the standard. This system dictates that each new "-illion" term is 1,000 times larger than the previous one.
The pattern is based on the Latin prefix for the power of 1000. For any number $N$, the corresponding "-illion" is $10^{(3 \times N) + 3}$. Septillion uses the Latin prefix *septi-* (seven), corresponding to $N=7$.
- Septillion: $10^{(3 \times 7) + 3} = 10^{24}$ (A thousand sextillion)
- Octillion: $10^{(3 \times 8) + 3} = 10^{27}$ (A thousand septillion)
Octillion, therefore, is the definitive answer in the short scale. It is a number so vast that it is difficult to contextualize, but it is the critical next step in the standard numerical sequence. The pattern continues using Latin prefixes, creating a predictable and elegant ladder of numerical values.
The Numerical Sequence After Septillion (Short Scale)
The following list details the names and numerical values that immediately follow septillion, all based on the short scale system where each step is a factor of $10^3$ (one thousand) larger than the last.
- Octillion: $10^{27}$ (1 followed by 27 zeros)
- Nonillion: $10^{30}$ (1 followed by 30 zeros, based on *nonus* for nine)
- Decillion: $10^{33}$ (1 followed by 33 zeros, based on *decem* for ten)
- Undecillion: $10^{36}$ (1 followed by 36 zeros, based on *undecim* for eleven)
- Duodecillion: $10^{39}$ (1 followed by 39 zeros, based on *duodecim* for twelve)
- Tredecillion: $10^{42}$ (1 followed by 42 zeros, based on *tredecim* for thirteen)
This systematic approach, utilizing Latin prefixes, allows mathematicians and scientists to name virtually any power of 10, though the names quickly become cumbersome and are usually replaced by scientific notation for practicality.
Navigating the Scales: Short vs. Long Scale Confusion
The primary source of ambiguity when discussing large numbers like septillion is the existence of two major naming conventions: the short scale and the long scale. This difference is not merely academic; it means the same word can represent wildly different numerical values in different parts of the world.
The Short Scale (U.S. and Modern Usage)
As established, the short scale is based on powers of a thousand ($10^3$). A billion is $10^9$, a trillion is $10^{12}$, and a septillion is $10^{24}$. The next step is always a jump of three zeros.
The Long Scale (Europe and Historical Usage)
The long scale, used historically in the UK and still common in many European countries, is based on powers of a million ($10^6$). In this system, a billion is defined as a million million ($10^{12}$), and a trillion is a million million million ($10^{18}$).
Crucially, the long scale introduces an intermediate term, the "-ard" (e.g., milliard, billiard, trilliard). A new "-illion" term is only used when the number is a million times larger than the previous one.
In the long scale:
- Billion (Short Scale $10^9$) is called a Milliard.
- Trillion (Short Scale $10^{12}$) is called a Billion.
- Septillion (Short Scale $10^{24}$) is called a Quadrillion.
Under the long scale system, the name "septillion" corresponds to $10^{42}$ (a 1 followed by 42 zeros, or a million sextillion). Therefore, if you are using the long scale, the number that comes after septillion ($10^{42}$) is Septilliard ($10^{45}$).
This historical and geographical difference highlights why clarity is paramount when discussing numerical nomenclature and numerical values of extremely large numbers.
Beyond the 'Illions': Numbers That Break the Mold
While the sequence of septillion, octillion, nonillion, and decillion follows a logical pattern, the human need to quantify the vastness of the universe and theoretical mathematics quickly pushes the limits of this system. These numbers transition from being merely large to becoming truly astronomical mathematical constants and entities.
The Limit of the Latin Prefixes: Centillion
The standard system of Latin prefixes continues all the way up to $N=100$, which gives us the Centillion. In the short scale, a centillion is $10^{303}$ (a 1 followed by 303 zeros). This number is often cited as the largest number with a single, commonly agreed-upon name derived from the standard "-illion" structure. While names exist for numbers beyond centillion, they are rarely used and involve complex combinations of Latin and Greek prefixes, such as *duocentillion* or *trecentillion*.
The Internet's Favorite Colossal Numbers: Googol and Googolplex
For true topical authority on large numbers, one must move past the structured "-illion" sequence and into the realm of custom-named numbers. These were created to illustrate the concept of infinity and the limits of computation.
1. Googol ($10^{100}$)
Coined in 1938 by the nine-year-old nephew of American mathematician Edward Kasner, a googol is a 1 followed by 100 zeros. While significantly smaller than a centillion ($10^{303}$), it is far larger than any number with a physical meaning, as the number of atoms in the observable universe is estimated to be only around $10^{80}$.
2. Googolplex ($10^{\text{Googol}}$)
The number that comes after a googol in terms of conceptual magnitude is the googolplex. It is defined as 10 raised to the power of a googol. This number is so large that it is impossible to write out in full, even if every particle in the universe were converted into ink and paper. The sheer size of the exponent (a googol) makes it one of the most famous examples of a number that transcends physical reality.
The Absolute Extremes: Graham's Number and Skewes' Number
To put octillion and even centillion into perspective, mathematics has defined numbers that make a googolplex look minuscule. These are known as truly gigantic numbers and are often required in advanced fields like Ramsey theory and number theory.
3. Graham's Number (G)
Graham's number is considered the largest number ever used in a serious mathematical proof. It is so immense that it cannot be expressed using standard exponential notation (like $10^{100}$). Instead, it requires Knuth's up-arrow notation, a system of hyper-operations. If you were to write out the digits of Graham's number, you would run out of space in the universe long before you finished the first exponent.
4. Skewes' Number
Skewes' number is another historical example of a massive number, originally defined as the upper bound for the first time the number of primes less than $x$ is greater than the logarithmic integral of $x$. Its initial value was so large that it was expressed as $e^{e^{e^{79}}}$, a tower of exponents that dwarfs any of the "-illions."
Conclusion: The Practicality of Scientific Notation
The question of "what comes after septillion" leads us from the simple answer of octillion into a complex debate over short scale vs. long scale systems and ultimately, into the realm of numbers that defy human comprehension. While the Latin-based "-illion" sequence provides a beautiful and systematic way to name increasingly large powers of 10, the practical limit of this numerical nomenclature is quickly reached.
In modern science, astronomy, and computation, the use of scientific notation—such as $10^{24}$ for septillion—replaces the cumbersome names entirely. This method is universal, unambiguous, and allows for the precise expression of any numerical value, from the smallest subatomic particles to the largest cosmological constants, ensuring that the pursuit of ever-larger numbers remains confined to the elegance of mathematics rather than the confusion of language.
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