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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

 Nominal 21 Cardinal twenty-one Ordinal 21st Number of digits 2 Sum of digits 3 Product of digits 2 Number parity Odd
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Prime Factorization of 21

 Prime factorization 3 x 7 Prime factors 3, 7 Number of distinct prime factors ω(n) 2 Total number of prime factors Ω(n) 2 Sum of prime factors 10 Product of prime factors 21
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Divisors of 21

 List of proper divisors 1, 3, 7 List of all dividers 1, 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.
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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
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Sequences

 Is 21 a Catalan number? No Is 21 a Fibonacci number? Yes Is 21 a Idoneal number? Yes: I15
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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
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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
20Vigesimal1120
36Base36l36
60SexagesimalL60
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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 21 4.58258 Natural Logarithm (ln) of 21 3.04452 Decimal Logarithm (log) of 21 1.32222
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Trigonometry

Trigonometry is the study of the relationship between the angles and sides of a triangle.
 Sine of 21 0.836656 Cosecant of 21 1.19523 Cosine of 21 -0.547729 Secant of 21 -1.82572 Tangent of 21 -1.5275 Cotangent of 21 -0.654665
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Number parity

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

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.
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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)
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Numeral systems

How to write 21 in other number systems?
 Bengali numerals ২১ Eastern Arabic numerals ٢١ Hieroglyphs numeralsused in Ancient Egypt 𓎇𓏺 Khmer numerals ២១ Japanese numerals 二十一 Roman numerals XXI Thai numerals ๒๑
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Translation

How do you say 21 in 38 different languages?
 Arabic واحد و عشرون Croatian dvadeset i jedan Czech dvacet jeden Danish en og tyve Dutch éénentwintig Estonian blaeve vɔ ɖekɛ Faroese tjúgo­ein Filipino dalawáng pû’t isá Finnish kaksi­kymmentä­yksi French vingt et un Greek είκοσι ένα German ein­und­zwanzig Hebrew עשרים ואחת Hindi इक्कीस Hungarian huszon­egy Icelandic tuttugu og einn Indonesian dua puluh satu Italian ventuno Japanese 二十一 Korean 이십일 Latvian divdesmit viens Lithuanian dvidešimt vienas Norwegian tjue­én Persian بیست و یک Polish dwadzieścia jeden Portuguese vinte e um Romanian douăzeci şi unu Russian двадцать один Serbian двадесет и један Slovak dvadsať­jeden Slovene dvaset ena Spanish veintiuno Swahili ishirini na moja Swedish tjugoen Thai ยี่​สิบ​เอ็ด Turkish yirmi bir Ukrainian двадцять один Vietnamese hai mươi mốt
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Miscellaneous

 Number 21 reversed 12 ASCII Code 21  Unicode Character U+0015  Unix Timestamp Thu, 01 Jan 1970 00:00:21 +0000
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