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.
- 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.
101 is part of
Factors & digit properties
- Divisors (2)
- 1, 101
- Prime factorisation
- 101
- Digit sum
- 2
- Digital root
- 2
Representations
- Decimal
- 101
- Binary
- 1100101
- Octal
- 145
- Hexadecimal
- 65
- Roman numeral
- CI
- Scientific notation
- 1.010 × 10^2
Other mathematical patterns
- Palindromic number
- Deficient number
- Twin prime
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
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: 3 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026