123
Port 123 carries NTP, the Network Time Protocol that keeps computer clocks synchronised.
- Odd
- Composite
Where 123 fits
Why 123 is special
Accurate time is a prerequisite for things that look unrelated to it: TLS certificates have validity windows, log correlation depends on ordering, and time-based one-time passwords fail outright when a clock drifts. NTP on port 123 is the service almost nothing notices until it stops.
Same number, different meanings
How 123 is understood across different contexts — never implying one meaning because of another.
- Mathematics
Accurate time is a prerequisite for things that look unrelated to it: TLS certificates have validity windows, log correlation depends on ordering, and time-based one-time passwords fail outright when a clock drifts. NTP on port 123 is the service almost nothing notices until it stops.
- Technology & computing
Lotus 1-2-3 was released in 1983 and was the application that sold the IBM PC into business. Its name referred to combining spreadsheet, database and charting in one product, and its dominance lasted until Excel displaced it.
- Everyday life
One-two-three is the standard way of saying that something is elementary, and 123 is among the most common weak passwords and default codes. Its predictability is precisely what makes it both a teaching device and a security problem.
Factors & digit properties
- Divisors (4)
- 1, 3, 41, 123
- Prime factorisation
- 3 × 41
- Digit sum
- 6
- Digital root
- 6
Representations
- Decimal
- 123
- Binary
- 1111011
- Octal
- 173
- Hexadecimal
- 7b
- Roman numeral
- CXXIII
- Scientific notation
- 1.230 × 10^2
Other mathematical patterns
- Deficient number
- Semiprime
- Lucas number
Related numbers & connections
NTP runs on port 123, and its legacy monitoring commands made those servers among the largest amplification sources recorded.
View 5905 →Technology & computing
Lotus 1-2-3 was released in 1983 and was the application that sold the IBM PC into business. Its name referred to combining spreadsheet, database and charting in one product, and its dominance lasted until Excel displaced it.
DocumentedTechnology & computingGeography: United States, sold internationallyPeriod: 1983–NTP on port 123 keeps clocks synchronised, and a surprising amount depends on that. Certificate validity windows, log correlation across machines and time-based one-time passwords all fail when a clock drifts far enough — usually presenting as an unrelated-looking authentication problem.
DocumentedTechnology & computing
Everyday life
One-two-three is the standard way of saying that something is elementary, and 123 is among the most common weak passwords and default codes. Its predictability is precisely what makes it both a teaching device and a security problem.
DocumentedEveryday lifeGeography: GlobalPeriod: long-standing
Common questions
Is 123 a prime number?
No, 123 is not prime.
What are the factors of 123?
The factors of 123 are 1, 3, 41, 123.
What is 123 in Roman numerals?
123 in Roman numerals is CXXIII.
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: 3 August 2026