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
- Scientific notation
- 1.230 × 10^2
Roman numerals
C X X I I I
Binary
1 1 1 1 0 1 1
1 × 64 + 1 × 32 + 1 × 16 + 1 × 8 + 0 × 4 + 1 × 2 + 1 × 1 = 123
Octal
1 7 3
1 × 64 + 7 × 8 + 3 × 1 = 123
Hexadecimal
7 b
7 × 16 + b × 1 = 123
Read as powers of two: 64 + 32 + 16 + 8 + 2 + 1 = 123.
In historical numeral systems
Egyptian
1 coil of rope, 2 hobbles, 3 strokes
1 × 100 + 2 × 10 + 3 × 1 = 123. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
2 vertical wedges (sixties place), 3 vertical wedges (units place)
2 × 60 + 3 = 123. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
rho, then kappa, then gamma, marked as a numeral
rho-kappa-gamma + keraia
rho + kappa + gamma 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 kaf, then gimel
qof-kaf-gimel
qof (100) + kaf (20) + gimel (3) = 123, written in descending order.
Maya
1 bar + 1 dot (upper, twenties place) over 3 dots (lower, units place)
6 × 20 + 3 = 123. 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
- 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: 15 July 2026