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.
165 connects to:
- numbers on earth — appears in
- 541 — contrasts with
Same number, different meanings
How 165 is understood across different contexts — never implying one meaning because of another.
- Mathematics
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.
- 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.
- Geography
The area of the Pacific Ocean is about 165 million square kilometres. Larger than all the land on Earth put together.
165 is part of
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
- Scientific notation
- 1.650 × 10^2
Roman numerals
C L X V
Binary
1 0 1 0 0 1 0 1
1 × 128 + 0 × 64 + 1 × 32 + 0 × 16 + 0 × 8 + 1 × 4 + 0 × 2 + 1 × 1 = 165
Octal
2 4 5
2 × 64 + 4 × 8 + 5 × 1 = 165
Hexadecimal
a 5
a × 16 + 5 × 1 = 165
Read as powers of two: 128 + 32 + 4 + 1 = 165.
In historical numeral systems
Egyptian
1 coil of rope, 6 hobbles, 5 strokes
1 × 100 + 6 × 10 + 5 × 1 = 165. 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), 4 corner wedges + 5 vertical wedges (units place)
2 × 60 + 45 = 165. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
rho, then xi, then epsilon, marked as a numeral
rho-xi-epsilon + keraia
rho + xi + epsilon 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 samekh, then he
qof-samekh-he
qof (100) + samekh (60) + he (5) = 165, written in descending order.
Maya
1 bar + 3 dots (upper, twenties place) over 1 bar (lower, units place)
8 × 20 + 5 = 165. 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
Related numbers & connections
165 appears in Numbers on Earth, the topic covering numbers that carry a documented earth-science or weather fact.
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 →Numbers Around Us
- appears inEarth
why?
Strength 0.50, confidence "high".
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
Geography
The area of the Pacific Ocean is about 165 million square kilometres. Larger than all the land on Earth put together.
DocumentedGeographyGeography: worldwide
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: 2 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026