11 (number)
From Academic Kids

11 (eleven) is the natural number following 10 and preceding 12. Eleven is the smallest positive integer requiring three syllables in English.
Template:Numbers 10s  

Cardinal  11 eleven 
Ordinal  11th eleventh 
Numeral system  
Factorization  prime 
Divisors  1, 11 
Roman numeral  XI 
Unicode representation of Roman numeral  Ⅺ, ⅺ 
Binary  1011 
Hexadecimal  B 
In mathematics
Eleven is the 5th smallest prime number. 11 is the fourth Sophie Germain prime, the third safe prime, and the first repunit prime. Although it is necessary for n to be prime for 2^{n}1 to be a Mersenne prime, the converse is not true: 2^{11}  1 = 2047 which is 23 × 89. The next prime is 13, with which it comprises a twin prime.
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 onedigit numbers all have double digits: 00 (=0), 11, 22, 33, 44 . . .
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.
In base 10, there is also an easy way of multiplying numbers by 11. 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 4117).
An elevensided polygon is a hendecagon.
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 Template:Num/neg, eleven is a Heegner number.
In science
 The atomic number of sodium.
In astronomy,
 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 (http://www.ngcic.org/) NGC 11, a spiral galaxy in the constellation Andromeda
 The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/LEsaros/LEsaros1175.html) 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 (http://sunearth.gsfc.nasa.gov/eclipse/LEsaros/LEsaros1175.html) 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.
In other fields
There are eleven players in a soccer as well as in a cricket team.
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).
Uri Geller has always been fascinated by the number eleven. After the September 11 World Trade Center attack, he published an open list of connections to the number eleven involved in that attack.
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 quote "Eleven! That's ridiculous, it's not even funny" from Negativland composition "Time Zones" (referring to the number of time zones in USSR) is referenced many times in multiplayer online game Kingdom of Loathing. As a result many KoL players say that phrase every time they encounter number 11 (often without knowing its true origins).
Eleven is:
 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.
 The number of spacetime dimensions in Mtheory.
 A page in the Service Record Book of an enlisted Marine for writing down disciplinary actions.
 In rugby union the left wing wears the 11 shirt.
 In Internet Explorer, the F11 key toggles full screen viewing mode
 Historical years: 11 A.D., 11 B.C., or 1911
 The number 11 bus is one of the best and cheapest ways of sightseeing in London
 The number of thumb keys on a bassoon, not counting the whisper key. (A few bassons have a twelfth thumb key).da:11 (tal)
de:Elf es:Once eo:Dek unu fr:11 (nombre) ko:11 ia:11 it:Undici he:11 (מספר) hu:11 (szám) nah:Mahtlahtlince nl:Elf (getal) ja:11 no:11 (tall) nn:Talet elleve pt:Onze sl:11 (število) sv:11 (tal) zh:11