27

27 is a natural number that follows 26 and precedes 28. It is an odd, composite number and a cube, since 27 = 3^3.

In base 10, its digits sum to 9, and 27 is divisible by 9, making it a Harshad number. Its divisors are 1, 3, 9, and 27. In Roman numerals it is written as XXVII, and in base 3 it is 1000_3.

27 is the atomic number of cobalt (Co). Cobalt is a transition metal used in alloys, batteries, catalysts, and medical applications; cobalt-60 is employed in radiotherapy and sterilization.

Culturally, the New Testament is commonly cited as containing 27 books. The Spanish alphabet is traditionally listed with 27 letters, including the letter ñ. The term 27 Club refers to a group of famous musicians who died at age 27, linking the number to a notable pop-culture motif.

In computing, the decimal value 27 corresponds to the Escape (ESC) control character in ASCII. The number 27 also appears in various mathematical and cultural contexts as a cube of 3.