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'101' ('one hundred and one') is the natural number following 100 and preceding 102. When written without the "and," 101 is the smallest non-negative integer requiring thirteen letters in English.

Cardinal	101 one hundred and one
Ordinal	101st one hundred and first
Factorization	''prime''
Roman numeral	CI
Binary	1100101
Hexadecimal	65

Contents

In mathematics

In science

In astronomy

In other fields

References

In mathematics

'101' is the 26th prime number and a palindromic number (therefore also a palindromic prime). The next prime is 103, with which it comprises a twin prime (making 101 a Chen prime). Because the period length of its reciprocal is unique among primes, 101 is a unique prime. 101 is an Eisenstein prime with no imaginary part and real part of the form $3n\; -\; 1$.
101 is the sum of five consecutive primes (13 + 17 + 19 + 23 + 29). Given 101, the Mertens function returns 0 (number). 101 is the fifth alternating factorial.
101 is a centered decagonal number.
For a 3-digit number in base 10, this number has a relatively simple divisibility test. The number is split into groups of four, starting with the rightmost four, and added up to produce a 4-digit number. If this 4-digit number is of the form 1000''a'' + 100''b'' + 10''a'' + ''b'' (where ''a'' and ''b'' are integers from 0 to 9), such as 3232 or 9797, or of the form 100''b'' + ''b'', such as 707 and 808, then the number is divisible by 101. This might not be as simple as the divisibility tests for numbers like 3 and 5, and it might not be terribly practical, but it is simpler than the divisibility tests for other 3-digit numbers.
On the seven-segment display of a calculator, 101 is both a strobogrammatic prime and a dihedral prime.

In science

★ The atomic number of mendelevium, an actinide.

★ In mineralogy, a Miller index of 101 is a crystal face that crosses the horizontal axis (a) and 3d vertical axis (c) but does not cross the 2d vertical axis (b).

In astronomy

★ The Messier object M101, a magnitude 8.5 spiral galaxy in the constellation Ursa Major, also known as the Pinwheel Galaxy

★ The New General Catalogue object NGC101, a magnitude 12.9 spiral galaxy in the constellation Sculptor

★ The Asteroid 101 Helena.

In other fields

'101' is also:

★ Room 101 in George Orwell's novel ''Nineteen Eighty-Four''.

★ "Neo's number" in the 1999 sci-fi action movie The Matrix, according to one of the producers in The Matrix Revisited. It is the number on numerous significant doors in the movie; for example it is Neo's flat number at the beginning of the movie.

★ At universities in the United States, Canada and South Africa, often the course number of basic or entry-level courses. By extension, it is informally used elsewhere to indicate things that are meant for beginners. At universities with four-digit course numbers, the equivalent course number is 1001 or 1010. This usage is not common in the rest of the world.

★ According to Books in Print, more books are now published with a title that begins with '101' than '100'. They usually describe or discuss a list of items, such as ''101 ways to...'' or ''101 questions and answers about...'' . This marketing tool is used to imply that the customer is given a little extra information beyond books that include only 100 items. Some books have taken this marketing scheme even further with titles that begin with '102', '103', or '1001'. The number is used in this context as a slang term when referring to "a 101 document" what is usually referred to as a statistical survey or overview of some topic. For example, ''101 Ways To Bug Your Teacher'', a book by Lee Wardlaw.

★ Taipei 101, The tallest building in the world.

★ ''The Hundred and One Dalmatians'' by Dodie Smith (and the various movie versions thereof).

★ The emergency telephone number for the police in Argentina.

★ The emergency telephone number for medical emergencies in Israel

★ '101', The Single Non-Emergency Number (SNEN), a new telephone number being rolled out across the United Kingdom. This is intended as an easy to remember number, for non emergency calls to the police on occasions when dialing 999 isn't appropriate. Calls are charged at a flat rate of 10p. (Official 101 Site)

★ ''101'', a live album and movie by Depeche Mode.

★ 101st kilometre, a condition of release from the Gulag in the Soviet Union

★ The (minimum) number of keys on a standard computer keyboard.

★ U.S. Route 101, which runs from California to Washington.

★ In DisneySpeak, a ride breakdown in a Disney theme park (an indirect reference to the US Route 101)

★ Unit 101 of the Israeli Defense Forces.

★ 101st Airborne Division of the United States Army

★ For new (US) checking accounts, the default number for the first check.

★ Room 101 is a Comedy series on BBC2 in the UK presented by Paul Merton.

★ The year AD 101 or 101 BC.

★ The famous orchestra 101 Strings.

★ "Back to the 101" is a song by Albert Hammond, Jr.

★ The space shuttle mission STS-101.

★ The trick-taking card game 101, in which the seniority of cards is: Five, Jack, Joker, Ace of Hearts, Ace of Trumps, High Red, Low Black.

★ The 101, an in-house channel on DirecTV's satellite service

★ The Orbiter Vehicle Designation for Shuttle ''Enterprise''

★ Martin 101 is a worldwide model, singer and artist. martin101 official web site

★ Arnold Schwarzenegger´s terminator model in The Terminator and in Terminator 2 was a T-800 Model 101.

★ 101 Was also a Robot built for the UK TV series Robot Wars, supposedlly costing only £1.01 to build

★ The Phrase "101" is used for an example on how to do or operate something at its most basic level. (eg. iPods 101 or Computers 101)

★ 101 is the HTTP status code indicating that a client should switch protocols (e.g. to HTTPS)
http://en.wikipedia.org/wiki/Land_Rover_101_Forward_Control

References

★ Wells, D. ''The Penguin Dictionary of Curious and Interesting Numbers'' London: Penguin Group. (1987): page 133