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20 (twenty) is a positive integer following 19 and preceding 21. Its ordinal form is written "20th" or "twentieth".

Properties Edit

20 is an even composite number.

20 is the 4th tetrahedral number.

20 is the smallest number with abundance 2.

The number eπ − π is almost equal to 20. The emphasis is on “almost”, since π and eπ are algebraically independent.

In googology Edit

In Greek-based number-naming systems, 20 is associated with prefix "icosa-", and with prefix "viginti-" in Latin systems.

20 is the base of a googologism by Sbiis Saibian called menger sponge. It is equal to 20^3###^^^###3 in Extended Cascading-E Notation.

Wiki user Denis Maksudov coined the name unalum for this number, and it's equal to \(f_1(10)\) using the fast-growing hierarchy.[1]

As a cash denomination Edit

Some currencies, such as the euro and the United States dollar, have banknotes with this number in the denomination.

20-0

Some currencies, such as the Czech koruna and the Hungarian forint, have coins with this number in the denomination.

In pope numbering Edit

Its Roman numeral (XX) has never been used in a name of a pope or an antipope, unlike all the other Roman numerals from I to XXIII. In particular, the papal name John XX has been skipped.

Sources Edit

  1. Traveling To The Infinity
Numbers by Denis Maksudov
Alpha series
Epsilon series
Epsilon(0)-addition series: Zeraddep · Unaddep · Baddep · Traddep · Quadraddep · Quintaddep · Sextaddep · Septaddep · Octaddep · Nonaddep · Dekaddep · Hektaddep · Kiladdep · Megaddep · Gigaddep · Teraddep · Petaddep · Exaddep · Zettaddep · Yottaddep
Epsilon(0)-multiplication series: Bultep · Trultep · Quadrultep · Quintultep · Sextultep · Septultep · Octultep · Nonultep · Dekultep · Hektultep · Kilultep · Megultep · Gigultep · Terultep · Petultep · Exultep · Zettultep · Yottultep
Epsilon(0)-exponentiation series: Bexep · Trexep · Quadrexep · Quintexep · Sextexep · Septexep · Octexep · Nonexep · Dekexep · Hektexep · Kilexep · Megexep · Gigexep · Terexep · Petexep · Exexep · Zettexep · Yottexep
Epsilon(0)-tetration series: Bitetrep · Tritetrep · Quadritetrep · Quintitetrep · Sextitetrep · Septitetrep · Octitetrep · Nonitetrep · Dekotetrep · Hektotetrep · Kilotetrep · Megotetrep · Gigotetrep · Terotetrep · Petotetrep · Exotetrep · Zettotetrep · Yottotetrep
Epsilon(1)-addition series: Unaddunep · Baddunep · Traddunep · Quadraddunep · Quintaddunep · Sextaddunep · Septaddunep · Octaddunep · Nonaddunep · Dekaddunep · Hektaddunep · Kiladdunep · Megaddunep · Gigaddunep · Teraddunep · Petaddunep · Exaddunep · Zettaddunep · Yottaddunep
Inserted epsilon series: Uninep · Binep · Trinep · Quadrinep · Quintinep · Sextinep · Septinep · Octinep · Noninep · Dekinep · Hektinep · Kilinep · Meginep · Giginep · Terinep · Petinep · Exinep · Zettinep · Yottinep
Inserted eta series
Phi series
\(I(\alpha,\beta)\) series
Initial \(I(\alpha,\beta)\) series: Unimah · Bimah · Trimah · Quadrimah · Quintimah · Sextimah · Septimah · Octimah · Nonimah · Dekimah · Hektimah · Kilimah · Megimah · Gigimah · Terimah · Petimah · Eximah · Zettimah · Yottimah
Inserted \(I(\alpha,\beta)\) series: Uninimah · Binimah · Trinimah · Quadrinimah · Quintinimah · Sextinimah · Septinimah · Octinimah · Noninimah · Dekinimah · Hektinimah · Kilinimah · Meginimah · Giginimah · Terinimah · Petinimah · Exinimah · Zettinimah · Yottinimah