We use cookies and other tracking technologies to improve your browsing experience on our website, to show you personalized content and targeted ads, to analyze our website traffic, and to understand where our visitors are coming from. For more information, please review our cookie policy and privacy policy.
By choosing I Accept, you consent to our use of cookies and other tracking technologies.

21

Number 21 (twenty-one) is an odd two-digits composite number and natural number following 20 and preceding 22.

Properties of the number 21

Nominal21
Cardinaltwenty-one
Ordinal21st
Number of digits2
Sum of digits3
Product of digits2
Number parityOdd
Calculation was done in 0.0000319481 seconds

Prime Factorization of 21

Prime factorization3 x 7
Prime factors3, 7
Number of distinct prime factors ω(n)2
Total number of prime factors Ω(n)2
Sum of prime factors10
Product of prime factors21
Calculation was done in 0.0000078678 seconds

Divisors of 21

List of proper divisors 1, 3, 7
List of all dividers1, 3, 7, 21
Number of divisors d(n)4
Sum of all divisors σ(n)32
Aliquot sum 11
21 is a deficient number , since it is larger than the sum of its proper divisors (11). Its deficiency is 10.
Calculation was done in 0.0000190735 seconds

Prime numbers

Is 21 a prime number?No
Is 21 a semiprime number?Yes
Is 21 a Chen prime number?No
Is 21 a Mersenne prime number?No
Calculation was done in 0.0000100136 seconds

Sequences

Is 21 a Catalan number?No
Is 21 a Fibonacci number?Yes
Is 21 a Idoneal number?Yes: I15
Calculation was done in 0.0000040531 seconds

Number theory

Number theory is a branch of pure mathematics devoted primarily to the study of the integers and integer-valued functions.
21 is not a Happy number
21 is a Humble number
21 is not a Münchhausen number
21 is not a Perfect number
21 is not a Perfect square
21 is not a Palindrome
Calculation was done in 0.0061841011 seconds

Numeric Bases of 21

In mathematics, a base or radix of a numeral system is the number of unique digits, including zero, used to represent numbers in that system.
BaseSystemValue
2Binary101012
3Ternary2103
4Quaternary1114
5Quinary415
6Senary336
7Septenary307
8Octal258
9Nonary239
10Decimal21
12Duodecimal1912
16Hexadecimal1516
20Vigesimal1120
36Base36l36
60SexagesimalL60
Calculation was done in 0.0000159740 seconds

Mathematical operations

Mathematical operations are actions that are performed on numbers or mathematical expressions to find a numerical result.
Square of 21 (n2)441
Cube of 21 (n3)9261
Square root of 214.5825756949558
Natural Logarithm (ln) of 213.0445224377234
Decimal Logarithm (log) of 211.3222192947339
Calculation was done in 0.0000050068 seconds

Trigonometry

Trigonometry is the study of the relationship between the angles and sides of a triangle.
Sine of 210.83665563853606
Cosecant of 211.1952348779359
Cosine of 21-0.54772926022427
Secant of 21-1.825719516227
Tangent of 21-1.5274985276366
Cotangent of 21-0.65466511548606
Calculation was done in 0.0000100136 seconds

Number parity

Parity is the property of an integer of whether it is even or odd.

Is 21 an Even Number?

No

Is 21 an Odd Number?

Yes, the number 21 is an odd number.
Total number of all odd numbers from 1 to 21 is 11
Sum of all the odd numbers from 1 to 21 are 121
The sum of all odd numbers is a perfect square: 121 = 11
An odd number is any integer (a whole number) that cannot be divided by 2 evenly. Odd numbers are the opposite of even numbers.
Calculation was done in 0.0000059605 seconds

Ban number

In recreational mathematics, a ban number is a number that does not contain a particular letter when spelled out in English; in other words, the letter is "banned".
The spelling of 21 in words is "twenty-one", meaning that:
21 is an aban number (a number without the letter a)
21 is not an eban number (as it contains the letter e)
21 is an iban number (a number without the letter i)
21 is not an oban number (as it contains the letter o)
21 is not a tban number (as it contains the letter t)
21 is an uban number (a number without the letter u)
Calculation was done in 0.0000021458 seconds

Numeral systems

How to write 21 in other number systems?
Bengali numerals২১
Eastern Arabic numerals٢١
Hieroglyphs numeralsused in Ancient Egypt𓎇𓏺
Khmer numerals២១
Japanese numerals二十一
Roman numeralsXXI
Thai numerals๒๑
Calculation was done in 0.0000779629 seconds

Translation

How do you say 21 in 38 different languages?
Arabicواحد و عشرون
Croatiandvadeset i jedan
Czechdvacet jeden
Danish en og tyve
Dutchéénentwintig
Estonianblaeve vɔ ɖekɛ
Faroesetjúgo­ein
Filipinodalawáng pû’t isá
Finnishkaksi­kymmentä­yksi
Frenchvingt et un
Greekείκοσι ένα
Germanein­und­zwanzig
Hebrewעשרים ואחת
Hindiइक्कीस
Hungarianhuszon­egy
Icelandictuttugu og einn
Indonesiandua puluh satu
Italianventuno
Japanese二十一
Korean이십일
Latviandivdesmit viens
Lithuaniandvidešimt vienas
Norwegiantjue­én
Persianبیست و یک
Polishdwadzieścia jeden
Portuguesevinte e um
Romaniandouăzeci şi unu
Russianдвадцать один
Serbianдвадесет и један
Slovakdvadsať­jeden
Slovenedvaset ena
Spanish veintiuno
Swahiliishirini na moja
Swedishtjugoen
Thaiยี่​สิบ​เอ็ด
Turkishyirmi bir
Ukrainianдвадцять один
Vietnamesehai mươi mốt
Calculation was done in 0.0138010979 seconds

Miscellaneous

Number 21 reversed12
ASCII Code21
Unicode CharacterU+0015
Unix TimestampThu, 01 Jan 1970 00:00:21 +0000
Calculation was done in 0.0000290871 seconds
This page was generated in 0.02 seconds.