27 (twenty-seven) is the natural number following 26 and preceding 28. Twenty-seven is the smallest positive integer requiring four syllables to name in English, though it can be unambiguously defined in just two: "three cubed". It is the first composite integer not divisible by any of its digits.

Cardinal	twenty-seven
Ordinal	twenty-seventh
Factorization
Roman numeral	XXVII
Binary	11011
Hexadecimal	1B

In mathematics

Twenty-seven is a perfect cube, being 3³ = 3 × 3 × 3. 27 is 3↑↑2 (using Knuth's up-arrow notation). It is also a decagonal number. It is the magic result of a prime reciprocal magic square of the multiples of 1/7. It is a Smith number and a Harshad number. It is the twenty-seventh (and twenty-eighth) digit in π. (3.141592653589793238462643383279502884197169399375105820974944592).

A 10,000-day-old person is 27 years old (and some months).

In science

• The atomic number of cobalt

In astronomy,

Messier object M27, a magnitude 7.5 planetary nebula in the constellation Vulpecula, also known as the Dumbbell Nebula.

The New General Catalogue object NGC 27 , a spiral galaxy in the constellation Andromeda

The Saros number of the solar eclipse series which began on -1993 March 9 and ended on -713 April 16. The duration of Saros series 27 was 1280.1 years, and it contained 72 solar eclipses.

The Saros number of the lunar eclipse series which began on -1944 July 17 and ended on -411 January 23. The duration of Saros series 27 was 1532.5 years, and it contained 86 lunar eclipses.

The 27th moon of Jupiter is Sinope.

In other fields

Twenty-seven is also:

• The total number of books in the New Testament of the Holy Bible.
• The number of letters in the Spanish alphabet
• The current number of Amendments to the United States Constitution.
• The age in years at which rock music stars Jim Morrison, Jimi Hendrix, Brian Jones, Janis Joplin and Kurt Cobain died.
• The code for international direct-dialed phone calls to South Africa.
• "Weird Al" Yankovic hides the number 27 somewhere in many of his songs and videos.
• I-27 is the designation for a US interstate highway in Texas.
• Historical years: 27 A.D., 27 B.C., or 1927