11 (number)

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. Eleven is the smallest positive integer requiring three syllables in English.

undeca- (from Latin)


Cardinal	11 eleven
Ordinal	11th eleventh
Numeral system
Factorization	prime
Divisors	1, 11
Roman numeral	XI
Unicode representation of Roman numeral	Ⅺ, ⅺ
prefixes	hendeca- (from Greek)
Binary	1011
Hexadecimal	B

In mathematics

Eleven is the 5th smallest 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. 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.

Because it has a reciprocal of unique period length among primes, 11 is the second unique prime. 11 goes into 99 exactly 9 times, so vulgar fractions with 11 in the denominator have two digit repeating sequences in their decimal expansions. Multiples of eleven by one-digit numbers all have double digits: 00 (=0), 11, 22, 33, 44 . . .

An eleven-sided polygon is called a hendecagon or undecagon.

In both base 6 and base 8, the smallest prime with a composite sum of digits is 11.

In base 10, there is a simple test to determine if an integer is divisible by 11: take every digit of the number located in odd position and add them up, then take the remaining digits and add them up. If the difference between the two sums is a multiple of 11, including 0, then the number is divisible by 11.

An easy way of multiplying numbers by 11 in base 10 is: If the number has:

1 digit - Replicate the digit (so 2 x 11 becomes 22).
2 digits - Add the 2 digits together and place the result in the middle (so 47 x 11 becomes 4 (11) 7=4 (1+10) 7=(4+1) 1 7=517).

In base thirteen and higher bases (such as hexadecimal), eleven is represented as B, where ten is A. In duodecimal, however, eleven is sometimes represented as E and ten as T.

Multiplied by , eleven is a Heegner number.

In science

The atomic number of sodium.
The number of spacetime dimensions in M-theory.

Astronomy

Apollo 11 was the first manned spacecraft to land on the moon.

The approximate periodicity is 11 years in sunspot cycle.

Messier object M11, a magnitude 7.0 open cluster in the constellation Scutum, also known as the Wild Duck Cluster.

The New General Catalogue object NGC 11, a spiral galaxy in the constellation Andromeda

The Saros number of the solar eclipse series which began on -2511 December 26 and ended on -1158 March 18. The duration of Saros series 11 was 1352.2 years, and it contained 76 solar eclipses.

The Saros number of the lunar eclipse series which began on -2389 June 19 and ended on -1037 September 8. The duration of Saros series 11 was 1352.2 years, and it contained 76 lunar eclipses.

The 11th moon of Jupiter is Himalia.

In music

The interval of an octave and a fourth is an eleventh. A complete eleventh chord has almost every note of a scale.
The number of thumb keys on a bassoon, not counting the whisper key. (A few bassons have a twelfth thumb key).

In sports

There are eleven players on a soccerteam on the field at a time as well as in a cricket team. Within a school or college, the phrases "the football XI" and "the cricket XI" generally refer to the first (best) team currently playing. Other teams are often referred to as "the second XI" etc.

An American football team also has eleven players on the field at one time during play.

The car number of Darrell Waltrip and Cale Yarborough when they won their NASCAR Winston Cup Series championships.

In rugby union the left wing wears the 11 shirt.

As a Squad number

11 is squad number (jersey number) of various sports people:

Earl Boykins, Denver Nuggets, basketballer
Ryan Giggs, Manchester United footballer
Daniel Vettori, New Zealand cricketer
Glenn McGrath, Australian cricketer
Andrew Flintoff, England cricketer.
Mark Messier, Edmonton Oilers, New York Rangers, Vancouver Canucks, retired hockey player

Traditionally, a left wing midfielder in football wears number 11. Less commonly, it is worn by strikers. Jonah Lomu wears the number when he plays for the All Blacks as he plays left wing (see rugby union above).

11 is also by quarterbacks, kickers, punter and wide receivers in American football's NFL. The only NFL team that has retired the #11 is the New York Giants, in honor of quarterback Phil Simms.

In the military

The number of guns in a gun salute to U.S. Army, Air Force and Marine Corps Brigadier Generals, and to Navy and Coast Guard Rear Admirals Lower Half.
The number of General Orders for Sentries in the Marine Corps.
A page in the Service Record Book of an enlisted Marine for writing down disciplinary actions.
World War I ended with an Armistice on November 11, 1918, which went into effect at 11:00 am-the 11th hour on the 11th day of the 11th month of the year. Armistice Day is still observed on November 11 of each year, although it is now called Veteran's Day in the United States and Remembrance Day in the Commonwealth of Nations and parts of Europe.

In technology

In Mozilla Firefox, Konqueror for KDE, and Internet Explorer for Windows, the function key F11 key toggles full screen viewing mode. In Mac OS X, F11 hides all open windows.
The windowing system for Unix computers is known as X11.

In other fields

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 (see Doomsday clock).
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" or "These go to eleven" in popular culture has come to refer to anything capable of being exploited to its utmost abilities, or to exceed them, such as a sound volume control. Similarly, the expression "turning it up to eleven" may refer to the act of taking something to an extreme. In 2002 the phrase entered the Shorter Oxford English Dictionary with the definition "up to maximum volume" ^*.
Ocean's Eleven is the name of two American films.
In Basque, hamaika ("eleven") has the double meaning of "infinite", probably from amaigabe, "endless", as in Hamaika aldiz etortzeko esan dizut! ("I told you infinite/eleven times to come!".
American Airlines flight 11, a Boston-Los Angeles flight which crashed into the North Tower of the World Trade Center after being hijacked by terrorists in New York, New York on September 11, 2001.
In tarot, card no. 11 is "Justice".
The number 11 bus is one of the best and cheapest ways of sightseeing in London

Historical years

11 A.D., 11 B.C., 1911, 2011, etc.

Integers | Numbers

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