Notable Properties of Specific Numbers
An upper bound on the processing rate embodied by the human brain, based on 1011 neurons with 10000 dentrites each and a firing rate of 1000 per second. A brute-force simulation of this could be done with about 1018 floating-point operations per second, although in practice an optimized simulation would probably be used instead, reducing that number to about 1014. See also 109.
A very rough estmate of the number of grains of sand on all of Earth's beaches. This is based on an estimated 50,000 km of beach coastline with average beach width of 30m and depth of 5m, with sand grains that are 1 mm3 in size. See also 3×1023 and 5.6×1024.
An estimate of the total number of insects living in the world.61
12157692622039623539 = 11 + 22 + 13 + 54 + ... + 319 + 920, the sum of its own digits raised to consecutive powers. See 135.
The square root of 2127. See 1597463007.
This number has two legends associated with it.
The first legend is ancient and concerns the origin of the game of chess. King Shirham of India offered the inventor of the game any reward he cared to name, and the inventor asked for wheat: 1 grain for the first square on the chessboard, 2 grains for the second, 4 for the third, 8 for the fourth and so on doubling each time. The king was surprised, thinking this request was almost insultingly modest (thinking it would only add up to a few bushels), but obliged and instructed his servants to measure out the inventor's reward. They spent some time trying to do this, and eventually realized that all the wheat in all the kingdoms in the world would not come close to the amount specified. The number of grains of wheat requested is 264 - 1. (That is over 400 times the world's total wheat production in the year 2003, assuming a grain of wheat is 20 cubic millimeters.)
The second legend was created by Edward Lucas, the inventor of the Tower of Hanoi game, in 1884. As this story goes, at the center of the world (or, in another version, at the top of a mountain in the Himalayas), is a set of three rods bearing golden discs. There are 64 discs, and they are all different sizes. When the world was created, they were stacked on one of the rods, with the largest at the bottom and the smallest at the top. Ever since then, the priests have worked continually transferring the discs from one rod to another. They can only move one disc at a time, and they are not allowed ever to put a larger disc on top of a smaller disc. When they succeed in stacking all 64 discs on the second rod in a single stack as they were when the world was created, the world will end. The number of steps required to carry out this process is 264 - 1.
The fact that the number comes up in these two different stories seems even more of a coincidence when you consider that in the chess legend, the number is the sum 1+2+22+23+...+262+263, whereas in the Lucas legend it is 264-1. These happen to be the same sum, but arrived at in two different ways.
This is 264 = 226 = (((((22)2)2)2)2)2.
There are two ways to define an operator that follows next after addition, multiplication and exponents. Both definitions specify a function that takes two numbers A and B, and whose value is
A ^ A ^ A ^ ... ^ A
where the number of A's is B. But there are two obvious ways to define this, depending on whether you evaluate it from right to left or from left to right:
((..((A^A)^A)^...)^A)^A or A^(A^(A^...^(A^A)..))
If you group the parentheses from the right, you get the hyper4 operator, which is generally accepted as a better definition. If you group the parentheses from the left, you get something that grows much more slowly, but still pretty fast, and which I studied quite a bit in high school (late 1970's). I used the somewhat confusing name "powerlog" to refer to the function, as in "2 powerlog 7 equals 264". If you denote the operation by "④", then
A④B = (((A ^ A) ^ A) ^ ... ) ^ A = AA(B-1)
One reason the hyper4 definition is chosen over this one is that hyper4 cannot be reduced to a simple formula like this. Like each of the functions before it, hyper4 cannot be defined as a simple finite combination of other "lower" functions.
As discussed above, the lower-valued hyper4 operator can be expressed in terms of a double exponent: A④B = AA(B-1) so it is easily extended to reals and complex numbers. For example, see 4979.003621.
(264 also happens to be the largest integer I have ever memorized, except for trivial ones like vigintillion.)
43252003274489856000 = 8!×37 × 12!×211 / 2 ≈ 4.3252×1019
The number of ways to arrange a 3×3×3 Rubik's Cube. The center cubelets are assumed to be stationary. The 8 corners can be arranged into any of the 8!=40320 possible positions, and all but one can be rotated into any of 3 different rotations (the total rotation of all 8 pieces always adds up to 360o); this gives a factor of 8!×37 for the corner pieces. There are 12 edge pieces, which can be put in 12!=479001600 possible positions, and there are 211 rotation combinations (due to another rotation constraint). An additional factor of 2 is lost because if you want to swap a single pair of corners, you must either have a third corner out of place, or swap a single pair of edges. Alternately, if any two edges are out of place, a third edge or a pair of corners must be out of place.
This number became a rather well-known example of "innumeracy", when the packaging of the puzzle (as sold in the United States by Ideal Toy Corporation) said that the puzzle had "over 3 billion combinations". While not technically wrong, it is quite an understatement to say the least the actual number of combinations is greater than the square of 3 billion. Apparently, the company thought that customers would not understand "over 43 quintillion" quite as well as "over 3 billion".
If the rotation and swap constraints are avoided by physically disassembling the cube, you get a number 12 times as large, 519024039293878272000=8!×38×12!×212.
This is the smallest 6-perfect number. Its divisors add up to exactly 6 times itself. Its prime factorization is: 215×35×52×72×11×13×17×19×31×43×257. This is the smallest case of a K-perfect number where K itself is a perfect number (-:
This is cited by Numberphile as being the number of ways to set up a military Enigma machine, the type used by the Nazis during World War II. Setting up the machine involved selecting 3 out of 5 rotors, setting the initial positions of the rotors, then connecting ten pairs of letters on the plugboard. As explained in the video, the number of combinations works out to 5×4×3×263×26!/(6!×10!×210).
The smallest power of 2 that contains each of the digits (0 through 9) at least once.
519024039293878272000 = 8!×38×12!×212 ≈ 5.1902×1020
See also zillion.
6670903752021072936960 = 220×38×5×7×27704267971 ≈ 6.6709×1021
This is the number of possible solution patterns to Sudoku puzzles, based on the normal baseline Sudoku requirements (one of each digit in each row, column, and 3×3 subsquare). The number has been calculated and verified by two independent researchers using different exhaustive counting (brute-force search) algorithms33. This number counts two patterns as distinct even if a "relabeling" (e.g. changing all 3s to 7s and vice-versa) would make them equivalent. Many arrangements do not make for very interesting puzzles because (for example) they might be unsolvable unless you supply a lot of numbers in one area of the grid, making for an uneven starting pattern. See also 362880, 3546146300288 and 5524751496156892842531225600.
The length in meters of a "megaparsec", a unit of distance used in astronomy when discussing the size of the entire observable universe and other large-scale features, such as the distances of quasars and other very distant objects. See also 5878625373183.6 and 3.08568025×1016.
31858749840007945920321 = 4224814 ≈ 3.1859×1022
This is 4224814, equal to 958004 +2175194 +4145604. This is the simplest known counterexample to the conjecture of Euler that an nth power cannot be expressed as the sum of less than n smaller nth powers. In this case it's the sum of 3 4th powers. Of course, it can never happen with a sum of two 3rd powers, because that would be a counterexample to Fermat's Last Theorem. See also 216.
The extraterrestrial population of the visible universe according to Thomas Dick in his 1840 work Sidereal Heavens and Other Subjects Connected with Astronomy, As Illustrative of the Character of the Deity and of a Infinity of Worlds. See also 21891974404480 and 3×1023.
This is an old estimate of the number of stars in the universe, based on the strip survey estimate of Dr. Simon Driver's team, announced in early 2004. The previous estimate was 3.2×1022, and the current estimate is closer to 3×1023.
See also 1097.
This is 26×35×53×72×11×13×17×19×23×29×31×37×41×43×47, and is the smallest number with over a million distinct factors (1032192 to be exact). See also 12, 840, 45360, 720720, 3603600, 245044800, 2054221614063184107682218077003539824552559296000 and 457936×10917.
A recent (2010) study by van Dokkum using the Keck telescope estimated that there are 300 sextillion stars in the visible universe. (Before that, the best guess was more like 7×1022). These numbers are really hard to estimate because astronomers cannot see most of the stars in our galaxy (due to clouds of dust, and because most stars are too faint) nor can they see most of the galaxies (for the same reasons) so there needs to be much statistical guess-work. Even the definitions of "star" and "visible universe" are subject to debate and change.
By coincidence, 3×1023 is about half a mole of stars. It also happens that if you try to take 3×1023 things and arrange them along a straight line stretching from our location to the edge of the visible universe, they would be almost exactly a mile apart (see 1609.344 and 4.45×1026). Of course, stars are much bigger than a mile (even those massive enough to have collapsed into a neutron star or stellar black hole) but it gives a sense of the relative size of the universe and how much empty space there is.
See also 1097.
Starting with a prime, you can often add a digit to the beginning to make another prime. For example: 7 → 17 → 317 → 6317 → 26317, etc. 357686312646216567629137 is the largest number in base 10 that you can get this way. If 0 is allowed as a digit, then the task of finding the largest has no well-defined solution. (There are many, arbitrarily large, primes similar to 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000003 = 10101+3). See also 33333331, 73939133, 381654729, and 3608528850368400786036725.
The current most-accurate form of the "Avogadro constant" that many of us learned in chemistry class as "6.02×1023". The (30) at the end of "6.02214179(30)" represents the standard uncertainty (error) in the value: It is a more concise way to say "6.02214179 plus or minus 0.00000030".
This is the number of carbon atoms in 12 grams of pure carbon, unbound and in ground state. In general it is very close to the number of atoms in N grams of an element with atomic weight N. (The term atomic weight has since been replaced by "relative atomic mass".) For different substances the correspondence varies slightly, primarily because of binding energy in the nucleus and mass of the electron. (Note that "atomic weight" is not the same as the integer "atomic number", which is hardly ever close enough to be useful.)
A lot of people identify the Avagadro number as the largest number they have had to use, or in many cases, actually memorize.
This number is polydivisible, meaning that for any N, its first N digits are divisible by N: 3 is divisible by 1, 36 is divisible by 2, 360 is divisible by 3, 3608 is divisible by 4, etc. There is no larger number with this property. See also 73939133, 381654729, and 30000600003.
Another very rough estimate of the number of grains of sand on all of Earth's beaches. This is based on an estimate that there are 7×1014 cubic meters of sand, and that a grain of sand is 1/8 of a mm3 in volume. See also 7.5×1018 and 3×1023.
A reader wrote to discuss the issue of whether certain well-defined, but really large numbers (like the Moser) can be said to "exist", given that there is no way to write out all their digits, or in some cases (like the Graham-Rothschild number), no exact representation in any easily understood notation.
I suggested a rather strict definition of existence, which we can call "actual physical existence":
A number exists only when there is an object that has that many things in it.
So for example, if there is a stone that contains exactly 21655649541169643693329642 atoms, then the number 21655649541169643693329642 can be said to exist, but once that stone gains or loses an atom the number 21655649541169643693329642 doesn't exist anymore.
This definition seems to depend on an observer (kind of like the "if a tree falls in a forest" argument) because if the stone isn't available how can we count the atoms?
Of course, the practical difficulty of counting atoms (see Hill et. al ) makes this definition pretty useless anyway. If we do ever manage to count atoms in stones, the same problem would still arise when considering larger numbers like the number of atoms in a planet.
Given that we can't even prove the physical existence of a large number like 21655649541169643693329642, I find it unnecessary to worry much about the existence or non-existence of larger numbers, particularly when they are rigorously defined.
Mathematicians tend to deal with types of existence that are very abstract, sometimes even too abstract for the philosophers. If they are willing to discuss a number and make definitive claims about it, then I feel that I can too.
For more on this and similar issues, see my discussion of superclasses.
24547284284866560000000000 has this special property shared with 2592:
24 54 72 84 28 48 66 56 00 00 00 00 00 = 24547284284866560000000000
See also 3×1023.
(Approximately) the power output of the Sun in watts.
1027 is one octillion. Walt Whitman used octillions, as well as several other large number names including decillions, sextillions, quintillions, quadrillions, trillions, ten billion and ten thousand, in his poetry.
If a standard 4-suit 52-card deck is shuffled (randomly) and the cards are dealt to four players, the odds of all four of them getting a full suit are 1 in 2235197406895366368301560000. This number is (52!)/(13!4×4!), because you first shuffle the deck (52!), then divide the cards into 4 groups of 13, but it doesn't matter what order the 13 cards in each hand are dealt (divide by 13! for each hand), and it also doesn't matter which player gets which suit (divide by 4!).
Approximate mass of the Earth, in grams. See also 1.988435×1033.
(Approximately) the number of atoms in a 70-kilogram (154-pound) human being. To calculate your number of atoms, multiply your weight in kilograms by 1026. See also 6.32×1028.
Approximate number of particles (protons, neutrons and electrons) in a 70-kilogram (154-pound) human being. This is the mass in grams times Avogadro's number times 1.5 (based on the approximation that the number of electrons is half the number of protons + neutrons).
Mass of the Sun in kilograms. The "(25)" indicates the estimate of the uncertainty in the number: 1.98892±0.00025. See 1057.
An estimate of the number of prokaryotes (tiny organisms without a nucleus, including bacteria) on the Earth123. Produced by William Whitman and colleagues at the university of Georgia, the estimate includes 26×1028 organisms within the top 8 meters of the ground, 12×1028 in the water and oceans, about 80×1028 on land but below the 8-meter point, and 355×1028 in the ocean floor. The same scientists measured the mutation rate and estimated that every 20 minutes, somewhere on Earth a new species of bacteria comes into existence. Since prokaryotes comprise the vast majority of all living cells6, 5×1030 is also the total population of living things on the planet.
See also 1014.
Erroneous version of Mayan Coba Stela 1 number; see 10331233010526315789473684112000.
10331233010526315789473684112000 = (2019-1)×(13/19)×203×18 ≈ 1.033×1031
The number of days represented in the Mayan date numbering system by the number 220.127.116.11.18.104.22.168.22.214.171.124.126.96.36.199.188.8.131.52.0.0.0.020, which uses base 20 in each position except the second to last (see 5126 and 1872000). There are 20 digits of "13" and four 0's. This appears in an inscription on Stela 1 at Coba in Yucátan (see  figure 3, columns M and N; also . The symbols in the top half are all 13's next to glyphs representing units of time each 20 times longer than the next, after that are zeros for the b'ak'tun, k'atun, tun and winal units, then "4 Ahau" and "8 Cumku" among some other glyphs).
The following table illustrates how the expression (2019-1)×(13/19)×203×18 is equal to 184.108.40.206.220.127.116.11.18.104.22.168.22.214.171.124.126.96.36.199.0.0.0.020. (If you don't get the "(13/19)" part, consider the fact that 555 equals (103-1)×(5/9). )
Following the same pattern, twenty 13's and four 0's is (2020-1)×(13/19)×203×18, which works out to 10331233010526315789473684112000.
The value is often given as 10331233010526315789473682240000, but that is 13×203×18 less, or 188.8.131.52.184.108.40.206.220.127.116.11.18.104.22.168.22.214.171.124.0.0.0.020, with nineteen 13's and five 0's.
See also 23040000000.
The smallest known set of 7 consecutive primes that are spaced an even distance apart starts with this number. The spacing is 210. This set of primes, called a "CPAP-7" (for "continuous primes in arithmetic progression"), was discovered by Laurent Fousse & Paul Zimmermann in 200421. It is probably not the smallest; these types of primes are much more common at larger sizes, and therefore an exhaustive search for the first one takes longer than a coordinated search for a larger one. It is suspected that the smallest is about 22 or 23 digits long. See also 47, 251, 9843019 and 121174811.
91409924241424243424241924242500 = 110 + 210 + 310 + 410 + ... + 99910 + 100010 ≈ 9.1409924...×1031
The sum of the 10th powers of the numbers from 1 to 1000. Notice the pattern in the digits sort of regular, yet sort of irregular.
Around the year 1690, Jacques Bernoulli was studying the task (which was common at the time) of computing sums of powers. In the process he discovered the Bernoulli numbers, and used his new formulas to quickly calculate this sum as a demonstration of the importance of his discovery.
The Bernoulli numbers appear as coefficients in infinite series for many things including the sums of powers, various other combinatoric formulas, the Gamma function, etc. The first few Bernoulli numbers are: B0=1, B1 = -1/2, B2=1/6, B3=0, B4=-1/30, B5=0, B6=1/42, B7=0, B8=-1/30, B9=0, B10=5/66, B11=0, B12=-691/2730, B13=0, B14=7/6, B15=0, B16=-3617/510, B17=0, B18=43867/798, B19=0, B20=-174611/330, B21=0, B22=854513/138, B23=0, B24=-236364091/2730, ... Notice that the odd Bernoulli numbers starting with B3 are all zero, and the even ones starting with B2 alternate in sign. Also, after a point the size of the numerator starts to grow quickly. To compute the Bernoulli numbers, most mathematicians use the "generating function" method:
f(x) = x / (ex-1) = SUMn=0...inf[Bn xn / n!]
The way you determine the Bn from this is by finding the value of the nth derivative of the function at 0, which is equivalent to calculating the coefficients of the Taylor series for the function:
f(x) = f(0) + f'(0) x / 1! + f''(0) x2 / 2! + f'''(0) x3 / 3! + ...
Since f(x) and each of its derivatives are undefined for x=0, you actually have to use the limit as x approaches 0. Or, you can use a symbolic math program for example, in Maxima type taylor(x/(%e^x-1),x,0,10); then multiply the nth coefficient by n!
If you don't want to go to all this trouble the Bernoulli numbers can also be calculated by a simple iterative algorithm:
B0 = 1
Bn = - n! SUMk=0..(n-1) [Bk/(k! (n+1-k)!)]
The sums for the first few Bn's expand out like so:
B1 = - 1! ( B0/(0!×2!) )
B2 = - 2! ( B0/(0!×3!) + B1/(1!×2!) )
B3 = - 3! ( B0/(0!×4!) + B1/(1!×3!) + B2/(2!×2!) )
The factorials get to be rather big pretty quickly. You can avoid such big numbers by using a different, less elegant iterative algorithm, illustrated here:
B0 = 1
B1 = - B0 / 2
B2 = (-3 B1 - B0) / 3
B3 = (6 B2 + 4 B1 + B0) / 4
B4 = (10 B3 - 10 B2 - 5 B1 - B0) / 5
B5 = (15 B4 - 20 B3 + 15 B2 + 6 B1 + B0) / 6
B6 = (21 B5 - 35 B4 + 35 B3 - 21 B2 - 7 B1 - B0) / 7
The B3 and following lines all fit a pattern: the coefficients of the Bn come from Pascal's triangle, and the signs alternate, except for the sign of B1 which should be inverted (to make it have the same sign as B2 and B0).
The temperature (in degrees Celsius) of the Universe at the time the forces began to be distinct, and the highest temperature that can be explained by theory (unless a theory of quantum gravity is developed, which would also explain the universe before the Planck time). The "(85)" is the error range.
According to Clifford Pickover , 1033 is the largest power of ten that can be expressed as the product of two numbers that each have no zero digits: 233 × 533 = 8589934592 × 116415321826934814453125 = 1033.
Walt Whitman used decillions, as well as several other large number names in his poetry (see 1027 for more). Other numbers mentioned in songs and literature include 525600, 8675309, 1010, and 4.28...×10369693099
Approximate mass of the Sun, in grams. See also 5.4×1027.
316912650057057350374175801344000001 ≈ 3.169×1035
One of the factors of 1010100+1 (see that entry for details).
419994999149149944149149944191494441 = 6480702115891070212
This number, discovered by Jacobson and Applegate at Carnegie Mellon University, is believed to be the largest square whose digits are all squares (1, 4 and 9). This number is about 4.199×1035; the discoverers determined there was no other smaller than 1042.
Ratio between the electric force and the gravitational force between a proton and an antiproton: G×mp2/(kee2), where G is the gravitational constant 6.67384×10-11, mp is the mass of the proton, ke is the Coloumb constant c2/107 and e is the unit charge 1.602176565×10-19.
In April 2007, certain websites began publishing an encryption key used in certain types of DVD and Blu-Ray discs. It is 128 binary bits, normally expressed as a 32-digit hexadecimal number, but if converted to decimal it is about 1.32562×1037. Under United States law one cannot possess or communicate this key (either explicitly or indirectly), so it has been called an "illegal number".
101097362223624462291180422369532000000 = 54! / ((9!)6) ≈ 1.0109×1038
115132219018763992565095597973971522401 ≈ 1.151322...×1038
The largest Armstrong or narcissistic number in base 10. It has 39 digits, and is the sum of the 39th powers of its digits. The reason there are no larger numbers is related to the fact that as the number of digits increases more and more 9's are required to get a sum that has N digits. For example, 1070 - 1 is a number consisting of 70 9's in a row, and the sum of the 70th powers of its digits is 70 × 970 ≈ 4.386051 × 1068, which is only 69 digits long. So there is no way any 70-digit number can be equal to the sum of the 70th powers of its digits. The reason we see the last number occur at 39 digits is because, when you get close to the limit, the number of big digits like 8's and 9's has to increase to make sure the sum will be big enough, but this means that there are a lot fewer combinations of digits to choose from. There are 10N N-digit numbers, but much less than 10N when you start requiring it to have lots of 8's and 9's. The sums of Nth powers are fairly evenly distributed, so the overall probability of getting a match decreases. See also 4679307774 and 153.
This is (Mp/n)2 where Mp = 2.17651(13)×10-8 kg is the Planck mass, and n is the mass of the neutron (using CODATA 2010 values 50). Its reciprocal is one common version of a gravitational coupling constant, in this case using the neutron as the unit mass. See 3.377368×1038.
See also 1.69326×1038.
This is (Mp/p)2 where Mp = 2.17651(13)×10-8 kg is the Planck mass, and p is the mass of the proton (using CODATA 2010 values 50). Its reciprocal is one common version of a gravitational coupling constant, in this case using the proton as the unit mass.
170141183460469231731687303715884105727 = 2127-1 ≈ 1.7014...×1038
This is a Mersenne prime, and the value of C4 in Catalan's sequence given by C0 = 2; Cn+1 = 2Cn - 1. The sequence starts: 2, 3, 7, 127, and then jumps to this value. All five are prime, and Catalan was conjecturing that all Cn are prime.
The primeness of this number was verified by Édouard Lucas in 1876. It was the largest prime ever found by hand calculations, and for 75 years was the largest known prime. This record was beaten in 1951 by Ferrier, who used a mechanical desk calculator; subsequent records have been set by electronic computer. 34
It is not known whether C5=2C4-1 is prime.
A Mersenne prime of the form 2M - 1 where M is also a Mersenne prime is called a "double Mersenne prime". This is the largest known double Mersenne prime. The next four candidates are 2213-1-1, 2217-1-1, 2219-1-1 and 2231-1-1, and are all known to be composite.
If you add the numbers in the Catalan sequence 3, 7, 127, 170141183460469231731687303715884105727, you get 3, 10, 137, 2127+136. The last of these is sort of vaguely close to the gravity to electric force ratio (if a ratio of 13 can be thought of as close; see also 1040), and the one before it (137) is famously close to the fine structure constant. Because of these two semi-coincidences, some physics theorists have explored the possibility of a Combinatorial hierarchy that can be used to generate most or all of the physical constants and properties of fundamental particles. (See , ,  and ).
Reader Mark Thomas suggested this number as possibly being related to the Dirac large numbers hypothesis. It is a value that appears as a dimensionless combination of physical constants and also as a combination of two numbers from pure mathematics. Given:
It is (almost) exactly equal to 702 (eπ√163)2 = 3.3773687587694...×1038. 4900 is connected to the Leech lattice (via a Lorentzian lattice II25,1 construction in 26 dimensions96), and eπ√163 (the Ramanujan constant) is closely related to the Monster group (which is definitely related to the Leech lattice due to Exceptional isomorphism). The Leech lattice might also be related to particle physics, if certain versions of string theory turn out to be true.
This coincidence can also be expressed as 702(eπ√163)2/2 = 1.6886843793...×1038 ≈ (Mp/n)2 1.68861(10)×1038 where Mp = 2.17651(13)×10-8 kg is the Planck mass, and n as before is the mass of the neutron; in this form it is easier to see why the value is unitless, because Mp and n are both in units of mass. See also 137.035 and 3.149544×1079.
This is (approximately) the maximum value that can be represented in the commonly-used IEEE 754 single-precision (1+8+23 bit) floating-point format.
Ratio between the strength of the gravitational and electric attraction of a proton and an electron. Based on CODATA values50, the fundamental charge e=1.602176565(35)×10-19 C, the electric constant ε0=8.854187817×10-12 Fm-1, the Newtonian constant of gravitation G=6.67384(80)×10-11 m3kg-1s-2, the mass of the proton mp=1.672621777(74)×10-27 kg, and the mass of the electron me=9.10938291(40)×10-31 kg; the ratio between the two forces is given by e2/(4πε0Gmpme). The numbers in parentheses give error ranges.
This number was considered significant by Paul Dirac, see 1040. Dirac put forth this hypothesis at a time when the proton was still considered fundamental (long before the quark model); note that for other similar pairs of particles (e.g. a proton and a muon, or a positron and an electron) you get different ratios. See also 1.23563×1036, 3.377×1038 and 1.786×1041.
Physicist Paul Dirac's estimate70 of the ratio of the universe's size to that of a proton. Using present-day values (see 1.73×10-15, 299792458 and 13.72×109) and a naive assumption that the universe grows at the speed of light, the number would be about 7×1039. Dirac noted that it was "close" to the ratio between the strength of gravity and electical attraction between a proton and an electron (about 2.2687×1039). He hypothesized that it is more than just coincidence, and proposed that the strength of gravity diminishes with time such that the two numbers remain the same. That would mean that when gravity and electricity were of equal strength the universe was about the size of a proton. The choice of the proton's radius is a bit arbitrary; compare to 8.03×1060, and see also 3.377×1038, and 3.1495...×1079.
I have also seen the use of the term "zillion" to refer to this quantity, such as in this quote by Robert Dalling in "The story of us humans ...":
"The electric force is very strong it is a zillion (1045) times as strong as the gravitational force."
In this context, the time it takes light to travel the distance across a proton (roughly 5.77×10-24) is sometimes called a "jiffy".
Quick index: if you're looking for a specific number, start with whichever of these is closest: 0.065988... 1 1.618033... 3.141592... 4 12 16 21 24 29 39 46 52 64 68 89 107 137.03599... 158 231 256 365 616 714 1024 1729 4181 10080 45360 262144 1969920 73939133 4294967297 5×1011 1018 5.4×1027 1040 5.21...×1078 1.29...×10865 1040000 109152051 101036 101010100 footnotes Also, check out my large numbers and integer sequences pages.