1665
1665 is the year of the Great Plague of London.
- Odd
- Composite
Where 1665 fits
Why 1665 is special
Around 100,000 people died, roughly a quarter of London's population, in the last major English outbreak of bubonic plague. The Great Fire followed the next year, and the claim that the fire ended the plague is repeated far more often than it is evidenced.
Same number, different meanings
How 1665 is understood across different contexts — never implying one meaning because of another.
- Mathematics
Around 100,000 people died, roughly a quarter of London's population, in the last major English outbreak of bubonic plague. The Great Fire followed the next year, and the claim that the fire ended the plague is repeated far more often than it is evidenced.
- History
In 1665, the Great Plague killed roughly a quarter of London's population (England).
- Science
In 1665, Robert Hooke's Micrographia described the compartments he saw in cork and gave them the name cells (England).
1665 is part of
Factors & digit properties
- Divisors (12)
- 1, 3, 5, 9, 15, 37, 45, 111, 185, 333, 555, 1665
- Prime factorisation
- 3^2 × 5 × 37
- Digit sum
- 18
- Digital root
- 9
Representations
- Decimal
- 1665
- Scientific notation
- 1.665 × 10^3
Roman numerals
M D C L X V
Binary
1 1 0 1 0 0 0 0 0 0 1
1 × 1,024 + 1 × 512 + 0 × 256 + 1 × 128 + 0 × 64 + 0 × 32 + 0 × 16 + 0 × 8 + 0 × 4 + 0 × 2 + 1 × 1 = 1,665
Octal
3 2 0 1
3 × 512 + 2 × 64 + 0 × 8 + 1 × 1 = 1,665
Hexadecimal
6 8 1
6 × 256 + 8 × 16 + 1 × 1 = 1,665
Read as powers of two: 1,024 + 512 + 128 + 1 = 1,665.
In historical numeral systems
Egyptian
1 lotus, 6 coils of rope, 6 hobbles, 5 strokes
1 × 1,000 + 6 × 100 + 6 × 10 + 5 × 1 = 1,665. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
2 corner wedges + 7 vertical wedges (sixties place), 4 corner wedges + 5 vertical wedges (units place)
27 × 60 + 45 = 1665. Places are separated by a space on the tablet, with the higher place written first.
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
The Great Fire followed London's plague year directly, and the claim that it ended the outbreak is repeated far more often than it is demonstrated.
View 1666 →Two plague outbreaks 300 years apart. The fourteenth-century pandemic killed a third to a half of Europe; the seventeenth-century London outbreak was a local recurrence of the same disease.
View 1347 →History
In 1665, the Great Plague killed roughly a quarter of London's population (England).
DocumentedHistoryGeography: EnglandPeriod: 1665The Great Plague killed around 100,000 people in London, roughly a quarter of its population, in the last major English bubonic plague outbreak. The Great Fire the following year is often credited with ending it, a claim repeated far more often than it is evidenced.
DocumentedHistoryGeography: London, EnglandPeriod: 1665
Science
In 1665, Robert Hooke's Micrographia described the compartments he saw in cork and gave them the name cells (England).
DocumentedScienceGeography: EnglandPeriod: 1665
Common questions
Is 1665 a prime number?
No, 1665 is not prime.
What are the factors of 1665?
The factors of 1665 are 1, 3, 5, 9, 15, 37, 45, 111, 185, 333, 555, 1665.
What is 1665 in Roman numerals?
1665 in Roman numerals is MDCLXV.
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