101

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. In the US, especially in academia, the number written or spoken with "and" is deprecated just like in "four and twenty" or "four score and seven"; "and" should only be used in a mixed number when traversing the decimal point or otherwise starting the fractional part after stating the integral part. The popularity of The 101 Dalmatians by British author, Dodie Smith, creates difficulty for US teachers in this regard.

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. 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 1000a + 100b + 10a + b (where a and b are integers from 0 to 9), such as 3232 or 9797, or of the form 100b + 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:

• The year AD 101 or 101 BC.
• At universities in Australia, Canada, South Africa, and the United States, 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 United Kingdom.
• 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.
• Room 101 in George Orwell's novel Nineteen Eighty-Four.
• Room 101, a BBC comedy television series, named after Orwell.

• "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.
• 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
• The Single Non-Emergency Number (SNEN), a new flat-rate telephone number being rolled out across the United Kingdom, intended as an easy to remember number, for non emergency calls to the police on occasions when dialing 999 is not appropriate. (official 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.
• 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
• 101 is the HTTP status code indicating that a client should switch protocols (e.g. to HTTPS)
• David Carradine's character Bill, in the Kill Bill movies, was living in room 101.
• Land Rover 101 Forward Control
• Number 101 is the highest number to be used to win a Formula 1 Grand Prix (Alberto Ascari 1953 German GP)
• DBAG 101s are a class of German electric locomotives.

References

• Wells, D. The Penguin Dictionary of Curious and Interesting Numbers London: Penguin Group. (1987): page 133zh-yue:101

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