# 27 (number): Map

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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."

## In mathematics

Twenty-seven is a perfect cube, being 3³ = 3 × 3 × 3. 27 is therefore the second smallest cube of a prime number. 27 is 23 (see tetration). There are exactly 27 straight lines on a smooth cubic surface. 27 is also a decagonal number.

27 has an aliquot sum of 13 and is the first composite member of the 13-aliquot tree with the aliquot sequence (27,13,1,0). Twenty-seven is the aliquot sum of the two odd discrete biprimes 69 and 133.

In base 10, it is the first composite number not evenly divisible by any of its digits. It is the radix (base) of the septemvigesimal positional numeral system.

In a prime reciprocal magic square of the multiples of 1/7, the magic constant is 27.

In the Collatz conjecture (aka the "3n + 1 conjecture") a starting value of 27 requires 112 steps to reach 1, many more than any lower number.

The unique simple formally real Jordan algebra, the exceptional Jordan algebra of self-adjoint 3 by 3 matrices of quaternions, is 27-dimensional.

In base 10, it is a Smith number and a Harshad number.

It is the twenty-eighth (and twenty-ninth) digit in π. (3.141592653589793238462643383279...).
If you start counting with 0 it is considered one of few Self-Locating strings in pi.

## In music

Wolfgang Mozart was born on January 27, 1756. He completed 27 concerti for piano and orchestra.

Many talented and famous rock/blues musicians died at age 27. These include Robert Johnson, Janis Joplin, Jimi Hendrix, Brian Jones, Jim Morrison, Ron "Pigpen" McKernan, Pete Ham, Richey Edwards, and Kurt Cobain. The musicians who died at this age are often referred to as the 27 Club.

There are many songs titled just "Twenty-Seven," so it will suffice to list the most famous: a song by Scottish band Biffy Clyro from their 2002 album, Blackened Sky; the song by the Dave Matthews Band "#27," which they began playing on their 2007 summer tour; the Lagwagon song on their album Double Plaidinum. Fall Out Boy also has a song titled 27 from the album Folie à Deux (2008).

The number also occurs buried in the lyrics without occurring in the title. American parodist "Weird Al" Yankovic hides the number in many of his songs and videos. Ben Weasel also likes to include the number in his songs for his bands Screeching Weasel and The Riverdales.

In the United States, the number 27 is associated with the East Bay punk scene. There is also a band from Boston simply called 27.

## In art

The Minneapolis-based artist Deuce 7 (a.k.a. Deuce Seven, Twenty Seven, 27).

## In other fields

Twenty-seven is also:

## Historical years

27 B.C., 27 A.D., 1827, 1927, 2027, etc.

## References

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