127
127 is the largest signed 8-bit integer, and the first octet of the loopback address 127.0.0.1.
- Odd
- Prime
Where 127 fits
Why 127 is special
127 is two familiar limits at once. It is 2⁷ − 1, so a signed byte counts no higher, which is why so many old games capped stats and item counts there. It is also the whole 127.0.0.0/8 block reserved for loopback — every address in it means 'this machine', though 127.0.0.1 is the one anyone types.
Same number, different meanings
How 127 is understood across different contexts — never implying one meaning because of another.
- Mathematics
127 is two familiar limits at once. It is 2⁷ − 1, so a signed byte counts no higher, which is why so many old games capped stats and item counts there. It is also the whole 127.0.0.0/8 block reserved for loopback — every address in it means 'this machine', though 127.0.0.1 is the one anyone types.
- Technology & computing
127.0.0.1 is the loopback address, and the whole 127.0.0.0/8 block is reserved for it — over sixteen million addresses for a function needing one. Traffic sent there never reaches a network interface, which is why local development works with no connection at all.
- Science
A signed 8-bit integer spans −128 to 127, so 127 is the ceiling of a great many counters, limits and field widths in older software and in embedded systems where a byte is still the natural unit.
- Media & popular culture
127 Hours dramatises a documented survival in which the outcome was widely known before release. Reports of audiences fainting are notable precisely because the ending held no surprise.
127 is part of
Factors & digit properties
- Divisors (2)
- 1, 127
- Prime factorisation
- 127
- Digit sum
- 10
- Digital root
- 1
Representations
- Decimal
- 127
- Binary
- 1111111
- Octal
- 177
- Hexadecimal
- 7f
- Roman numeral
- CXXVII
- Scientific notation
- 1.270 × 10^2
Other mathematical patterns
- Deficient number
- Lucky number (mathematical sieve)
- Mersenne prime
Related numbers & connections
A local web server is reached at 127.0.0.1 on whichever port it binds, which is how development happens with no network at all.
View 80 →Technology & computing
127.0.0.1 is the loopback address, and the whole 127.0.0.0/8 block is reserved for it — over sixteen million addresses for a function needing one. Traffic sent there never reaches a network interface, which is why local development works with no connection at all.
DocumentedTechnology & computingGeography: International — IANA and IETFPeriod: 1981–The entire 127.0.0.0/8 block — over sixteen million addresses — is reserved for loopback, and every one of them refers to the machine you are on. Only 127.0.0.1 is used in practice. The reservation is why a program can talk to itself over the network without any network existing.
DocumentedTechnology & computing
Science
A signed 8-bit integer spans −128 to 127, so 127 is the ceiling of a great many counters, limits and field widths in older software and in embedded systems where a byte is still the natural unit.
DocumentedScienceGeography: GlobalPeriod: 1960s–
Media & popular culture
127 Hours dramatises a documented survival in which the outcome was widely known before release. Reports of audiences fainting are notable precisely because the ending held no surprise.
DocumentedMedia & popular cultureGeography: United StatesPeriod: 2010
Common questions
Is 127 a prime number?
Yes, 127 is prime — it has exactly two positive divisors: 1 and itself.
What are the factors of 127?
The factors of 127 are 1, 127.
What is 127 in Roman numerals?
127 in Roman numerals is CXXVII.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 4 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 3 August 2026