1666
1666 is the year of the Great Fire of London.
- Even
- Composite
Where 1666 fits
Why 1666 is special
The fire destroyed some 13,200 houses and most of the medieval city in four days, with a recorded death toll in single figures that historians consider a substantial undercount. It also ended the plague outbreak of the previous year, though the connection is more often asserted than demonstrated.
Same number, different meanings
How 1666 is understood across different contexts — never implying one meaning because of another.
- Mathematics
The fire destroyed some 13,200 houses and most of the medieval city in four days, with a recorded death toll in single figures that historians consider a substantial undercount. It also ended the plague outbreak of the previous year, though the connection is more often asserted than demonstrated.
- History
In 1666, the Great Fire destroyed much of the City of London (England).
- Science
In 1666, Newton passed sunlight through a prism and showed that white light is a mixture of colours rather than a pure thing the glass stained (England).
1666 is part of
Factors & digit properties
- Divisors (12)
- 1, 2, 7, 14, 17, 34, 49, 98, 119, 238, 833, 1666
- Prime factorisation
- 2 × 7^2 × 17
- Digit sum
- 19
- Digital root
- 1
Representations
- Decimal
- 1666
- Scientific notation
- 1.666 × 10^3
Roman numerals
M D C L X V I
Binary
1 1 0 1 0 0 0 0 0 1 0
1 × 1,024 + 1 × 512 + 0 × 256 + 1 × 128 + 0 × 64 + 0 × 32 + 0 × 16 + 0 × 8 + 0 × 4 + 1 × 2 + 0 × 1 = 1,666
Octal
3 2 0 2
3 × 512 + 2 × 64 + 0 × 8 + 2 × 1 = 1,666
Hexadecimal
6 8 2
6 × 256 + 8 × 16 + 2 × 1 = 1,666
Read as powers of two: 1,024 + 512 + 128 + 2 = 1,666.
In historical numeral systems
Egyptian
1 lotus, 6 coils of rope, 6 hobbles, 6 strokes
1 × 1,000 + 6 × 100 + 6 × 10 + 6 × 1 = 1,666. 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 + 6 vertical wedges (units place)
27 × 60 + 46 = 1666. 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
- Happy 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 1665 →The Great Fire of 1666 and the Great Storm of 1703 were both London catastrophes, and Defoe's account of the second assembled eyewitness reports into recognisably modern journalism.
View 1703 →History
In 1666, the Great Fire destroyed much of the City of London (England).
DocumentedHistoryGeography: EnglandPeriod: 1666The Great Fire destroyed around 13,200 houses and most of the medieval City of London in four days, with an official death toll in single figures that historians treat as a substantial undercount of the poor and unrecorded. The claim that it ended the previous year's plague is asserted more often than it is demonstrated.
DocumentedHistoryGeography: London, EnglandPeriod: 1666
Science
In 1666, Newton passed sunlight through a prism and showed that white light is a mixture of colours rather than a pure thing the glass stained (England).
DocumentedScienceGeography: EnglandPeriod: 1666
Common questions
Is 1666 a prime number?
No, 1666 is not prime.
What are the factors of 1666?
The factors of 1666 are 1, 2, 7, 14, 17, 34, 49, 98, 119, 238, 833, 1666.
What is 1666 in Roman numerals?
1666 in Roman numerals is MDCLXVI.
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