101
101 is a prime number widely used as shorthand for 'the basics' of any subject (as in 'Economics 101'), and in the UK it's the number to call the police for non-emergencies.
- Odd
- Prime
Where 101 fits
Why 101 is special
101 is a palindromic prime that's also a twin prime (paired with 103), but its everyday fame comes from two unrelated conventions: a 1929 US college course-numbering scheme that made '101' cultural shorthand for 'introductory', and the UK's dedicated non-emergency police number.
Same number, different meanings
How 101 is understood across different contexts — never implying one meaning because of another.
- Mathematics
101 is a palindromic prime that's also a twin prime (paired with 103), but its everyday fame comes from two unrelated conventions: a 1929 US college course-numbering scheme that made '101' cultural shorthand for 'introductory', and the UK's dedicated non-emergency police number.
- Everyday life
'101' is widely used as shorthand for an introductory course or the basics of any subject (as in 'Economics 101'). The usage traces to US collegiate three-digit course-numbering conventions, first attested in a 1929 University of Buffalo course catalogue, which standardised so that comparable introductory courses across institutions shared the same number.
- History
Introductory university courses in the United States were numbered 101 under a scheme that used the first digit for year of study. The number passed into general English as a term for the basics of any subject.
- Science
Mendelevium was the first element discovered by identifying single atoms. Naming it for Mendeleev acknowledges that his table predicted elements before anyone found them.
- Technology & computing
101 is the HTTP status Switching Protocols — the server agreeing to change the connection to something else, most commonly a WebSocket. It is the mechanism by which a page stops making requests and starts holding an open two-way channel, so almost every live chat and multiplayer browser game begins with a 101.
- Culture
American universities numbered first-year introductory courses 101 under schemes where the leading digit marks the year. The convention left academia and now functions as an ordinary English word for a basic introduction.
- Law & regulation
The non-emergency police telephone number in England, Wales, Scotland and Northern Ireland is 101 (United Kingdom).
- Media & popular culture
Room 101 in Nineteen Eighty-Four contains whatever the prisoner most fears, individually chosen. Orwell reportedly named it after a meeting room at the BBC. The phrase now works in ordinary British English as a place to consign things one cannot stand, which is a long way from its origin.
- Symbolic meaning
In modern numerology, 101 is treated as a 'new beginnings' number, combining the initiating energy attributed to 1 with 0 as an amplifier, and is said to reduce to 2 (1+0+1=2). This is a belief-system interpretation, not an empirical claim.
Not just a mathematical number
101is also used in ways where ordinary arithmetic doesn't apply — each listed below with what genuinely does and doesn't follow from it.
- Mathematical number
A genuine quantity — its mathematical properties (prime, square, factors, and so on) are real facts about it.
A genuine quantity that ordinary arithmetic applies to — it can be prime, even, a perfect square, added to another number meaningfully, and so on.
- Code
Also used as a code — HTTP status codes.
An assigned identifier from a fixed registry or standard — its digits don't represent an amount, and arithmetic on it is meaningless (HTTP status 404 + 1 is not a 'better' status; it's a different, unrelated code).
101 is part of
Factors & digit properties
- Divisors (2)
- 1, 101
- Prime factorisation
- 101
- Digit sum
- 2
- Digital root
- 2
Representations
- Decimal
- 101
- Scientific notation
- 1.010 × 10^2
Roman numerals
C I
Binary
1 1 0 0 1 0 1
1 × 64 + 1 × 32 + 0 × 16 + 0 × 8 + 1 × 4 + 0 × 2 + 1 × 1 = 101
Octal
1 4 5
1 × 64 + 4 × 8 + 5 × 1 = 101
Hexadecimal
6 5
6 × 16 + 5 × 1 = 101
Read as powers of two: 64 + 32 + 4 + 1 = 101.
In historical numeral systems
Egyptian
1 coil of rope, 1 stroke
1 × 100 + 1 × 1 = 101. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
1 vertical wedge (sixties place), 4 corner wedges + 1 vertical wedge (units place)
1 × 60 + 41 = 101. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
rho, then alpha, marked as a numeral
rho-alpha + keraia
rho + alpha written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
qof, then alef
qof-alef
qof (100) + alef (1) = 101, written in descending order.
Maya
1 bar (upper, twenties place) over 1 dot (lower, units place)
5 × 20 + 1 = 101. Places stack vertically with the smallest at the bottom, so the upper group is worth twenty times the lower.
Systems that simply cannot reach this value are left out. Where a script needs a font most readers do not have, the reading is given instead of the glyphs — see number systems for each system in full.
Other mathematical patterns
- Palindromic number
- Deficient number
- Twin prime
Related numbers & connections
101 immediately follows 100, the round decimal 'century' milestone.
View 100 →101 appears in Numbers in law and public systems, the topic covering numbers that carry a documented law or public-systems fact.
Introductory courses were numbered 101 under a scheme where the first digit gave the year of study.
View 100 →Nearby in a sequence
- is adjacent to100
why?
Strength 0.50, confidence "high".
Numbers Around Us
- appears inLaw and public systems
why?
Strength 0.50, confidence "high".
- is used byUK police non-emergency number (101)
why?
Strength 0.50, confidence "high".
- is used byEmergency telephone numbers
why?
Strength 0.50, confidence "high".
- is used byIntroductory-course numbering ('101')
why?
Strength 0.50, confidence "high".
- appears inHTTP status codes
why?
Strength 0.50, confidence "high".
Everyday life
'101' is widely used as shorthand for an introductory course or the basics of any subject (as in 'Economics 101'). The usage traces to US collegiate three-digit course-numbering conventions, first attested in a 1929 University of Buffalo course catalogue, which standardised so that comparable introductory courses across institutions shared the same number.
Widely documentedEveryday lifeGeography: United States (origin); now used internationally in English101 is the single non-emergency contact number for every police force in England and Wales, used for reports and enquiries that don't require an immediate response — distinct from 999, the emergency number.
DocumentedEveryday lifeGeography: England and Wales
History
Introductory university courses in the United States were numbered 101 under a scheme that used the first digit for year of study. The number passed into general English as a term for the basics of any subject.
DocumentedHistoryGeography: United States, then international EnglishPeriod: 1920s–
Science
Mendelevium was the first element discovered by identifying single atoms. Naming it for Mendeleev acknowledges that his table predicted elements before anyone found them.
DocumentedSciencePeriod: 1955
Technology & computing
101 is the HTTP status Switching Protocols — the server agreeing to change the connection to something else, most commonly a WebSocket. It is the mechanism by which a page stops making requests and starts holding an open two-way channel, so almost every live chat and multiplayer browser game begins with a 101.
DocumentedTechnology & computing
Culture
American universities numbered first-year introductory courses 101 under schemes where the leading digit marks the year. The convention left academia and now functions as an ordinary English word for a basic introduction.
DocumentedCultureGeography: United States and Canada
Law & regulation
The non-emergency police telephone number in England, Wales, Scotland and Northern Ireland is 101 (United Kingdom).
DocumentedLaw & regulationGeography: United Kingdom
Media & popular culture
Room 101 in Nineteen Eighty-Four contains whatever the prisoner most fears, individually chosen. Orwell reportedly named it after a meeting room at the BBC. The phrase now works in ordinary British English as a place to consign things one cannot stand, which is a long way from its origin.
DocumentedMedia & popular cultureGeography: United Kingdom
Symbolic meaning
In modern numerology, 101 is treated as a 'new beginnings' number, combining the initiating energy attributed to 1 with 0 as an amplifier, and is said to reduce to 2 (1+0+1=2). This is a belief-system interpretation, not an empirical claim.
Belief / interpretationSymbolic meaningPresented as belief or tradition, not as an established fact.
Common questions
Why is 101 used for introductory courses?
It comes from a US collegiate three-digit course-numbering convention — the Oxford English Dictionary's earliest citation is a 1929 University of Buffalo course catalogue. Standardising made it easy to compare introductory courses across schools, and '101' eventually became general shorthand for 'the basics' of any subject.
What is police number 101 for?
In England and Wales, 101 is the number to call any police force for non-emergencies — reporting a crime that isn't in progress, giving information, or general enquiries. It's free to call and distinct from 999, the emergency number.
Is 101 a prime number?
Yes — and it's also a palindrome (reads the same forwards and backwards) and a twin prime, paired with 103 (a prime exactly two away).
What are the factors of 101?
The factors of 101 are 1, 101.
What is 101 in Roman numerals?
101 in Roman numerals is CI.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 9 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026