101 (number)
Encyclopedia
101 is the natural number
Natural number
In mathematics, the natural numbers are the ordinary whole numbers used for counting and ordering . These purposes are related to the linguistic notions of cardinal and ordinal numbers, respectively...

following 100
100 (number)
100 is the natural number following 99 and preceding 101.-In mathematics:One hundred is the square of 10...

and preceding 102
102 (number)
102 is the natural number following 101 and preceding 103.-In mathematics:102 is an abundant number and semiperfect number. It is a sphenic number...

.

It is variously pronounced "one hundred and one" / "a hundred and one", "one hundred one" / "a hundred one", and "one oh one". As an ordinal number
Ordinal number (linguistics)
In linguistics, ordinal numbers are the words representing the rank of a number with respect to some order, in particular order or position . Its use may refer to size, importance, chronology, etc...

, 101st rather than 101th is the correct form.

In mathematics

101 is the 26th prime number
Prime number
A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. A natural number greater than 1 that is not a prime number is called a composite number. For example 5 is prime, as only 1 and 5 divide it, whereas 6 is composite, since it has the divisors 2...

and a palindromic number
Palindromic number
A palindromic number or numeral palindrome is a 'symmetrical' number like 16461, that remains the same when its digits are reversed. The term palindromic is derived from palindrome, which refers to a word like rotor that remains unchanged under reversal of its letters...

(and so a palindromic prime
Palindromic prime
A palindromic prime is a prime number that is also a palindromic number. Palindromicity depends on the base of the numbering system and its writing conventions, while primality is independent of such concerns...

). The next prime is 103
103 (number)
103 is the natural number following 102 and preceding 104.-In mathematics:One hundred [and] three is the 27th prime number. The previous prime is 101, making them both twin primes...

, with which it makes a twin prime
Twin prime
A twin prime is a prime number that differs from another prime number by two. Except for the pair , this is the smallest possible difference between two primes. Some examples of twin prime pairs are , , , , and...

pair, making 101 a Chen prime
Chen prime
A prime number p is called a Chen prime if p + 2 is either a prime or a product of two primes. The even number 2p + 2 therefore satisfies Chen's theorem....

. Because the period length of its reciprocal is unique among primes, 101 is a unique prime
Unique prime
In number theory, a unique prime is a certain kind of prime number. A prime p ≠ 2, 5 is called unique if there is no other prime q such that the period length of the decimal expansion of its reciprocal, 1 / p, is equivalent to the period length of the reciprocal of q, 1 / q...

. 101 is an Eisenstein prime
Eisenstein prime
In mathematics, an Eisenstein prime is an Eisenstein integerz = a + b\,\omega\qquadthat is irreducible in the ring-theoretic sense: its only Eisenstein divisors are the units , a + bω itself and its associates.The associates and the complex conjugate...

with no imaginary part and real part of the form .

101 is the sum of five consecutive primes (13
13 (number)
13 is the natural number after 12 and before 14. It is the smallest number with eight letters in its name spelled out in English. It is also the first of the teens – the numbers 13 through 19 – the ages of teenagers....

+ 17
17 (number)
17 is the natural number following 16 and preceding 18. It is prime.In spoken English, the numbers 17 and 70 are sometimes confused because they sound similar. When carefully enunciated, they differ in which syllable is stressed: 17 vs 70...

+ 19
19 (number)
19 is the natural number following 18 and preceding 20. It is a prime number.In English speech, the numbers 19 and 90 are often confused. When carefully enunciated, they differ in which syllable is stressed: 19 vs 90...

+ 23
23 (number)
23 is the natural number following 22 and preceding 24.- In mathematics :Twenty-three is the ninth prime number, the smallest odd prime that is not a twin prime. Twenty-three is also the fifth factorial prime, the third Woodall prime...

+ 29
29 (number)
29 is the natural number following 28 and preceding 30.-In mathematics:It is the tenth prime number, and also the fourth primorial prime. It forms a twin prime pair with thirty-one, which is also a primorial prime. Twenty-nine is also the sixth Sophie Germain prime. It is also the sum of three...

). Given 101, the Mertens function returns 0
0 (number)
0 is both a numberand the numerical digit used to represent that number in numerals.It fulfills a central role in mathematics as the additive identity of the integers, real numbers, and many other algebraic structures. As a digit, 0 is used as a placeholder in place value systems...

. 101 is the fifth alternating factorial
Alternating factorial
In mathematics, an alternating factorial is the absolute value of the alternating sum of the first n factorials.This is the same as their sum, with the odd-indexed factorials multiplied by −1 if n is even, and the even-indexed factorials multiplied by −1 if n is odd, resulting in an...

.

101 is a centered decagonal number
Centered decagonal number
A centered decagonal number is a centered figurate number that represents a decagon with a dot in the center and all other dots surrounding the center dot in successive decagonal layers...

.

The smallest prime for which 2^p-1 has not been completely factored.

For a 3-digit number in base 10, this number has a relatively simple divisibility test
Divisibility rule
A divisibility rule is a shorthand way of discovering whether a given number is divisible by a fixed divisor without performing the division, usually by examining its digits...

. The candidate 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 or 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
Seven-segment display
A seven-segment display , or seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot-matrix displays...

of a calculator, 101 is both a strobogrammatic prime
Strobogrammatic prime
A strobogrammatic prime is a prime number that, given a base and given a set of glyphs, appears the same whether viewed normally or upside down. In base 10, given a set of glyphs where 0, 1 and 8 are symmetrical around the horizontal axis, and 6 and 9 are the same as each other upside down, A...

and a dihedral prime
Dihedral prime
A dihedral prime or dihedral calculator prime is a prime number that still reads like itself or another prime number when read in a seven-segment display, regardless of orientation , and surface...

.

In science

• In mineralogy
Mineralogy
Mineralogy is the study of chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.-History:Early writing...

, a Miller index
Miller index
Miller indices form a notation system in crystallography for planes and directions in crystal lattices.In particular, a family of lattice planes is determined by three integers h, k, and ℓ, the Miller indices. They are written , and each index denotes a plane orthogonal to a direction in the...

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 physics and chemistry, it is the atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

of mendelevium
Mendelevium
Mendelevium is a synthetic element with the symbol Md and the atomic number 101. A metallic radioactive transuranic element in the actinide series, mendelevium is usually synthesized by bombarding einsteinium with alpha particles. It was named after Dmitri Ivanovich Mendeleev, who created the...

, an actinide.

In books

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
Slang
Slang is the use of informal words and expressions that are not considered standard in the speaker's language or dialect but are considered more acceptable when used socially. Slang is often to be found in areas of the lexicon that refer to things considered taboo...

term when referring to "a 101 document" what is usually referred to as a statistical survey
Statistical survey
Survey methodology is the field that studies surveys, that is, the sample of individuals from a population with a view towards making statistical inferences about the population using the sample. Polls about public opinion, such as political beliefs, are reported in the news media in democracies....

or overview of some topic.

Room 101
Room 101
Room 101 is a place introduced in the novel Nineteen Eighty-Four by George Orwell. It is a torture chamber in the Ministry of Love in which the Party attempts to subject a prisoner to his or her own worst nightmare, fear or phobia....

is a torture chamber in the novel Nineteen Eighty-Four
Nineteen Eighty-Four
Nineteen Eighty-Four by George Orwell is a dystopian novel about Oceania, a society ruled by the oligarchical dictatorship of the Party...

by George Orwell
George Orwell
Eric Arthur Blair , better known by his pen name George Orwell, was an English author and journalist...

.

In other fields

• 101 Ranch Oil Company
101 Ranch Oil Company
Founded in 1908 by oil exploration pioneer E. W. Marland, The 101 Ranch Oil Company was located on the famous Miller Brothers 101 Ranch and headquartered in Ponca City, Oklahoma...

• Taipei 101
Taipei 101
Taipei 101 , formerly known as the Taipei World Financial Center, is a landmark skyscraper located in Xinyi District, Taipei, Taiwan. The building ranked officially as the world's tallest from 2004 until the opening of the Burj Khalifa in Dubai in 2010...

, the tallest skyscraper in the world from 2004 to 2010.
• 101st kilometre
101st kilometre
101st kilometre is a colloquial name for the law restricting freedom of movement in the Soviet Union.In the Soviet Union, the rights of an inmate released from the prison would typically still be restricted for a long period of time...

, a condition of release from the Gulag
Gulag
The Gulag was the government agency that administered the main Soviet forced labor camp systems. While the camps housed a wide range of convicts, from petty criminals to political prisoners, large numbers were convicted by simplified procedures, such as NKVD troikas and other instruments of...

in the Soviet Union.
• Roi Et Province
Roi Et Province
Roi Et is one of the provinces of Thailand, located in the North-East of Thailand. Neighboring Provinces are Kalasin, Mukdahan, Yasothon, Sisaket, Surin and Maha Sarakham....

, a province in Thailand. The name is literally 101 in Thai language.
• An HTTP status code indicating that a client should switch protocols (e.g. to HTTPS
Https
Hypertext Transfer Protocol Secure is a combination of the Hypertext Transfer Protocol with SSL/TLS protocol to provide encrypted communication and secure identification of a network web server...

).
• The first course in a subject taught at a college
College
A college is an educational institution or a constituent part of an educational institution. Usage varies in English-speaking nations...

or university
University
A university is an institution of higher education and research, which grants academic degrees in a variety of subjects. A university is an organisation that provides both undergraduate education and postgraduate education...

in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

, or the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. By extension, "Topic 101" is used generally to indicate the basics of any subject. Used this way, it is always pronounced "one-oh-one". See Course number
Course number
A course number is the number given to a course at college or university. There are several conventions used at many institutions in North America:* Course numbers are three digits long....

.
• For a new checking account in the US, the number of the first check
Cheque
A cheque is a document/instrument See the negotiable cow—itself a fictional story—for discussions of cheques written on unusual surfaces. that orders a payment of money from a bank account...

.
• A term used to define the number of keys on a computer keyboard
Computer keyboard
In computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches...

• An emergency telephone number
Emergency telephone number
Many countries' public telephone networks have a single emergency telephone number, sometimes known as the universal emergency telephone number or occasionally the emergency services number, that allows a caller to contact local emergency services for assistance. The emergency telephone number may...

in Argentina, Belarus, Belgium, India, and Israel.
• 101 is the Single Non-Emergency Number (SNEN) in some parts of the UK, a telephone number used to call emergency services that are urgent but not emergencies.
• iCar 101 is a roadable aircraft design concept.
• 101 Dalmatians
The Hundred and One Dalmatians
The Hundred and One Dalmatians, or the Great Dog Robbery is a 1956 children's novel by Dodie Smith. A sequel entitled The Starlight Barking continues from the end of the first novel....

• The Zastava 101 is a compact car by the former Yugoslav automaker.
• Highways numbered 101, the longest and most well-known of which is U.S. Route 101
U.S. Route 101
U.S. Route 101, or U.S. Highway 101, is an important north–south U.S. highway that runs through the states of California, Oregon, and Washington, on the West Coast of the United States...

.
• the number 101 has a very important symbolic meaning to the Western Literary Society VNICA, the oldest student society in Amsterdam
• Rihanna - Rockstar 101
• Vault 101 is the starting area of Fallout 3
Fallout 3
Fallout 3 is an action role-playing game released by Bethesda Game Studios, and the third major installment in the Fallout series. The game was released in North America, Europe and Australia in October 2008, and in Japan in December 2008 for Microsoft Windows, PlayStation 3 and Xbox 360...

• Lebanese Red Cross EMS Center at Spears is coded 101
• In gematria
Gematria
Gematria or gimatria is a system of assigning numerical value to a word or phrase, in the belief that words or phrases with identical numerical values bear some relation to each other, or bear some relation to the number itself as it may apply to a person's age, the calendar year, or the like...

, a system of assigning numerical value to a word or phrase, 101 is the numerical value of the name מִיכָאֵל (Michael
Michael
Michael is a given name that comes from the , derived from the Hebrew question מי כמו אלוהים? meaning "Who is like God?" In English, it is sometimes shortened to Mike, Mikey, or, especially in Ireland, Mick...

in English)
• 101 is the identifying number of several infantry units in various militaries across the world, such as the American and Israeli paratrooper brigades