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

Properties of the number 81

Number of digits2
Sum of digits9
Product of digits8
Number parityOdd
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Prime Factorization of 81

Prime factorization3 x 3 x 3 x 3
Prime factorization in exponent form34
Prime factors3
Number of distinct prime factors ω(n)1
Total number of prime factors Ω(n)4
Sum of prime factors3
Product of prime factors3
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Divisors of 81

List of proper divisors 1, 3, 9, 27
List of all dividers1, 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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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.
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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 819
Natural Logarithm (ln) of 814.3944491546724
Decimal Logarithm (log) of 811.9084850188786
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Trigonometry is the study of the relationship between the angles and sides of a triangle.
Sine of 81-0.62988799427445
Cosecant of 81-1.5875838388567
Cosine of 810.77668598202163
Secant of 811.2875216279778
Tangent of 81-0.81099441583189
Cotangent of 81-1.2330541129241
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Number parity

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

Is 81 an Even Number?


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 numerals৮১
Eastern Arabic numerals٨١
Hieroglyphs numeralsused in Ancient Egypt𓎍𓏺
Khmer numerals៨១
Japanese numerals八十一
Roman numeralsLXXXI
Thai numerals๘๑
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How do you say 81 in 38 different languages?
Arabicواحد و ثمانون
Croatianosamdeset i jedan
Czechosmdesát jeden
Danish en og firs
Estonianblaenyi vɔ ɖekɛ
Filipinowalóng pû’t isá
Greekογδόντα ένα
Hebrewשמונים ואחת
Icelandicáttatíu og einn
Indonesiandelapan puluh satu
Latvianastoņdesmit viens
Lithuanianaštuoniasdešimt vienas
Persianهشتاد و یک
Polishosiemdziesiąt jeden
Portugueseoitenta e um
Romanianoptzeci şi unu
Russianвосемьдесят один
Serbianосамдесет и један
Sloveneosemdeset ena
Spanish ochenta y uno
Swahilithemanini na moja
Turkishseksen bir
Ukrainianвісімдесят один
Vietnamesetám mươi mốt
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Number 81 reversed18
Unicode CharacterU+0051Q
Unix TimestampThu, 01 Jan 1970 00:01:21 +0000
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