165
165 is the year the Antonine Plague reached Rome.
- Odd
- Composite
Where 165 fits
Why 165 is special
It killed perhaps five million people over fifteen years, including an emperor. Galen described it, and the pathogen is most often identified as smallpox without that being settled.
Factors & digit properties
- Divisors (8)
- 1, 3, 5, 11, 15, 33, 55, 165
- Prime factorisation
- 3 × 5 × 11
- Digit sum
- 12
- Digital root
- 3
Representations
- Decimal
- 165
- Binary
- 10100101
- Octal
- 245
- Hexadecimal
- a5
- Roman numeral
- CLXV
- Scientific notation
- 1.650 × 10^2
Other mathematical patterns
- Deficient number
Related numbers & connections
The Antonine Plague from 165 and the Plague of Justinian from 541 are the two great pandemics of the classical Mediterranean. The pathogen of the first is still not identified; the second has been confirmed as Yersinia pestis from ancient DNA.
View 541 →Other connections
- contrasts with541
why?
Strength 0.50, confidence "high".
History
The Antonine Plague from 165 is documented by Galen in clinical detail and still cannot be assigned a pathogen with confidence. Smallpox is the usual candidate and measles has been argued.
DocumentedHistoryGeography: Roman EmpirePeriod: 165–180
Common questions
Is 165 a prime number?
No, 165 is not prime.
What are the factors of 165?
The factors of 165 are 1, 3, 5, 11, 15, 33, 55, 165.
What is 165 in Roman numerals?
165 in Roman numerals is CLXV.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 1 reviewer-confirmed record, sourced and reviewed before publication.
Last reviewed: 3 August 2026