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 number not divisible by any of its digits. It is the radix (base) of the septemvigesimal positional numeral system.
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. There are exactly 27 straight lines on a cubic surface. It is the twenty-eighth (and twenty-ninth) digit in π. (3.141592653589793238462643383279).
A 10,000-day-old person is 27 years old.
Twenty-seven is also:
- The atomic number of cobalt.
- 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 musicians Robert Johnson, Jim Morrison, Jimi Hendrix, Kristen Pfaff, Chris Bell, Jason Thirsk, Brian Jones, Janis Joplin and Kurt Cobain died. Occasionally, this is termed the ideal age to die, and in fact the concept is so famous that it has inspired a brand of clothing, Dead.At.27.
- 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.
- With the number 37, a key number in comedian Charles Fleischer's concept of moleeds.
- I-27 is the designation for a US interstate highway in Texas.
- US 27 is the designation of a highway from Fort Wayne, Indiana to Miami, Florida.
- The number of completed, numbered piano concertos of Wolfgang Amadeus Mozart
- Historical years: 27 A.D., 27 B.C., or 1927
- The name of the second track on, and first single released from, the Biffy Clyro album Blackened Sky
- The name of a popular cigarette, Marlboro Blend No. 27