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# 81

Number 81 (eighty-one) is an odd two-digits composite number and natural number following 80 and preceding 82.

## Properties of the number 81

 Nominal 81 Cardinal eighty-one Ordinal 81st Number of digits 2 Sum of digits 9 Product of digits 8 Number parity Odd
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## Prime Factorization of 81

 Prime factorization 3 x 3 x 3 x 3 Prime factorization in exponent form 34 Prime factors 3 Number of distinct prime factors ω(n) 1 Total number of prime factors Ω(n) 4 Sum of prime factors 3 Product of prime factors 3
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## Divisors of 81

 List of proper divisors 1, 3, 9, 27 List of all dividers 1, 3, 9, 27, 81 Number of divisors d(n) 5 Sum of all divisors σ(n) 121 Aliquot sum 40 81 is a deficient number , since it is larger than the sum of its proper divisors (40). Its deficiency is 41.
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## Prime numbers

 Is 81 a prime number? No Is 81 a semiprime number? No Is 81 a Chen prime number? No Is 81 a Mersenne prime number? No
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## Sequences

 Is 81 a Catalan number? No Is 81 a Fibonacci number? No Is 81 a Idoneal number? No
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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.
 81 is not a Happy number 81 is a Humble number 81 is not a Münchhausen number 81 is not a Perfect number 81 is a Perfect square 81 is not a Palindrome
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## Numeric Bases of 81

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
2Binary10100012
3Ternary100003
4Quaternary11014
5Quinary3115
6Senary2136
7Septenary1447
8Octal1218
9Nonary1009
10Decimal81
12Duodecimal6912
20Vigesimal4120
36Base362936
60Sexagesimal1L60
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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 81 (n2) 6561 Cube of 81 (n3) 531441 Square root of 81 9 Natural Logarithm (ln) of 81 4.39445 Decimal Logarithm (log) of 81 1.90849
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## Trigonometry

Trigonometry is the study of the relationship between the angles and sides of a triangle.
 Sine of 81 -0.629888 Cosecant of 81 -1.58758 Cosine of 81 0.776686 Secant of 81 1.28752 Tangent of 81 -0.810994 Cotangent of 81 -1.23305
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## Number parity

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

No

### Is 81 an Odd Number?

Yes, the number 81 is an odd number.
Total number of all odd numbers from 1 to 81 is 41
Sum of all the odd numbers from 1 to 81 are 1681
The sum of all odd numbers is a perfect square: 1681 = 41
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 81 in words is "eighty-one", meaning that: 81 is an aban number (a number without the letter a) 81 is not an eban number (as it contains the letter e) 81 is not an iban number (as it contains the letter i) 81 is not an oban number (as it contains the letter o) 81 is not a tban number (as it contains the letter t) 81 is an uban number (a number without the letter u)
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## Numeral systems

How to write 81 in other number systems?
 Bengali numerals ৮১ Eastern Arabic numerals ٨١ Hieroglyphs numeralsused in Ancient Egypt 𓎍𓏺 Khmer numerals ៨១ Japanese numerals 八十一 Roman numerals LXXXI Thai numerals ๘๑
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## Translation

How do you say 81 in 38 different languages?
 Arabic واحد و ثمانون Croatian osamdeset i jedan Czech osmdesát jeden Danish en og firs Dutch éénentachtig Estonian blaenyi vɔ ɖekɛ Faroese áttati­ein Filipino walóng pû’t isá Finnish kahdeksan­kymmentä­yksi French quatre-vingt-un Greek ογδόντα ένα German ein­und­achtzig Hebrew שמונים ואחת Hindi इक्यासी Hungarian nyolcvan­egy Icelandic áttatíu og einn Indonesian delapan puluh satu Italian ottantuno Japanese 八十一 Korean 팔십일 Latvian astoņdesmit viens Lithuanian aštuoniasdešimt vienas Norwegian åtti­én Persian هشتاد و یک Polish osiemdziesiąt jeden Portuguese oitenta e um Romanian optzeci şi unu Russian восемьдесят один Serbian осамдесет и један Slovak osemdesiat­jeden Slovene osemdeset ena Spanish ochenta y uno Swahili themanini na moja Swedish åttioen Thai แปด​สิบ​เอ็ด Turkish seksen bir Ukrainian вісімдесят один Vietnamese tám mươi mốt
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## Miscellaneous

 Number 81 reversed 18 ASCII Code 81 Q Unicode Character U+0051 Q Unix Timestamp Thu, 01 Jan 1970 00:01:21 +0000
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