555
555 is the telephone prefix reserved for fiction in North America.
- Odd
- Composite
Where 555 fits
Why 555 is special
Numbers beginning 555-01 are not assigned to anyone, so films and television can show a number without directing calls at a real household. Before the convention, real people received years of calls from viewers.
Same number, different meanings
How 555 is understood across different contexts — never implying one meaning because of another.
- Mathematics
Numbers beginning 555-01 are not assigned to anyone, so films and television can show a number without directing calls at a real household. Before the convention, real people received years of calls from viewers.
- Technology & computing
The 555 has been in continuous production since 1972 and is still made in enormous volume. Its persistence is economic rather than technical: a purpose-built alternative costs more to design than the part costs to buy.
- Media & popular culture
Only 555-0100 to 555-0199 are genuinely reserved, not the whole 555 prefix. The convention exists because real subscribers were repeatedly harassed after their numbers appeared on screen.
Factors & digit properties
- Divisors (8)
- 1, 3, 5, 15, 37, 111, 185, 555
- Prime factorisation
- 3 × 5 × 37
- Digit sum
- 15
- Digital root
- 6
Representations
- Decimal
- 555
- Binary
- 1000101011
- Octal
- 1053
- Hexadecimal
- 22b
- Roman numeral
- DLV
- Scientific notation
- 5.550 × 10^2
Other mathematical patterns
- Palindromic number
- Deficient number
- Repdigit
- Harshad (Niven) number
Related numbers & connections
The 555 timer's part number is among the most recognised in electronics, and the chip is never called anything else.
The 741 op-amp and the 555 timer are the two chips almost every electronics course begins with, both introduced around 1970 and both still manufactured in volume.
View 741 →Numbers Around Us
- appears inNumbers assigned as identifiers
why?
Strength 0.50, confidence "high".
Technology & computing
The 555 has been in continuous production since 1972 and is still made in enormous volume. Its persistence is economic rather than technical: a purpose-built alternative costs more to design than the part costs to buy.
DocumentedTechnology & computingPeriod: 1972
Media & popular culture
Only 555-0100 to 555-0199 are genuinely reserved, not the whole 555 prefix. The convention exists because real subscribers were repeatedly harassed after their numbers appeared on screen.
DocumentedMedia & popular cultureGeography: United States and Canada
Common questions
Is 555 a prime number?
No, 555 is not prime.
What are the factors of 555?
The factors of 555 are 1, 3, 5, 15, 37, 111, 185, 555.
What is 555 in Roman numerals?
555 in Roman numerals is DLV.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 2 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 3 August 2026