11 (eleven) is the natural number following 10 and preceding 12. Because eleven is the first number which cannot be represented by a human using his or her ten fingers, it is often considered a mysterious number.
Also, eleven is the smallest positive integer requiring three syllables in English.
Eleven is the 5th smallest prime number. It is the smallest two-digit prime number. 11 is the fourth Sophie Germain prime, the third safe prime, the fourth Lucas prime, and the first repunit prime. Although it is necessary for n to be prime for 2n-1 to be a Mersenne prime, the converse is not true: 211 - 1 = 2047 which is 23 × 89. (but I don't get this...) The next prime is 13, with which it comprises a twin prime. 11 is an Eisenstein prime with no imaginary part and real part of the form 3n − 1. Displayed on a calculator, 11 is a strobogrammatic prime and a dihedral prime because it reads the same whether the calculator is turned upside down or reflected on a mirror, or both. (Blimey!)
Eleven is the atomic number of sodium (Sodium!! imagine!).
In chemistry, Group 11 includes the three coinage metals copper, silver, and gold known from antiquity.
The number of spacetime dimensions in M-theory. (help!)
The number eleven is important in numerology, as it is the first of
the Master Numbers.
Being only one hour before 12:00—midnight—the eleventh hour means the last possible moment to take care of something, and often implies a situation of urgent danger or emergency.
In Astrology, Aquarius is the 11th astrological sign of the Zodiac.
In the film This Is Spinal Tap, guitarist Nigel Tufnel proudly shows off an amplifier with top settings of 11, higher than the traditional 10. The phrase "Up to eleven" in popular culture has come to refer to anything capable of being exploited to its utmost abilities, or to exceed them. Similarly, the expression "turning it up to eleven" may refer to the act of taking something to an extreme.
More than you ever wanted to know about eleven.
One person meets another one in London