27 (number)
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27 is a natural number that follows 26 and precedes 28. It is a composite number, meaning it has divisors other than 1 and itself: 1, 3, 9, and 27.
The most notable property of 27 is that it is the third cube—that is, 3 × 3 × 3. It is also the only composite cube less than 64. In base 10, the digits 2 and 7 sum to 9, which is a divisor of 27—a property arising from the divisibility rule for 9.
Mathematical properties
27 can be written as 3³, making it a perfect cube but not a perfect square. The sum of its proper divisors—1, 3, and 9—is 13, which is less than 27; therefore 27 is a deficient number. It is also a number with base 3 that is easily expressed in base 3 notation: 27 = 1000 in base 3.
Other properties include the fact that 27 is the sum of the digits of cubes of small numbers when added in various ways, and it is one of the perfect totient numbers, which relate to iterating Euler's totient function (φ).
Representation and notation
In Roman numerals, 27 is written as XXVII. In Somali, it is called labaatan iyo toddoba. In computer systems, 27 is 11011 in binary (base 2) and 1B in hexadecimal (base 16).
Social use and measurement
27 appears in various systems of measurement and notation: it is the number of letters in some alphabets, it serves as part of year numbers (such as 1927 or 2027 when abbreviated), and it is used in country telephone codes (South Africa uses +27). Such uses rest on social convention rather than arising from the mathematical properties of the number.