1691
1691 is a year in the 17th century. The Treaty of Limerick ended the Williamite War in Ireland.
- Odd
- Composite
Where 1691 fits
Why 1691 is special
1691 has a profile because of what happened in it rather than because of any property of the number: the Treaty of Limerick ended the Williamite War in Ireland (Ireland).
1691 is part of
Factors & digit properties
- Divisors (4)
- 1, 19, 89, 1691
- Prime factorisation
- 19 × 89
- Digit sum
- 17
- Digital root
- 8
Representations
- Decimal
- 1691
- Scientific notation
- 1.691 × 10^3
Roman numerals
M D C X C I
MDCXCI uses the subtractive pair XC: ten before a hundred — a hundred minus ten.
Binary
1 1 0 1 0 0 1 1 0 1 1
1 × 1,024 + 1 × 512 + 0 × 256 + 1 × 128 + 0 × 64 + 0 × 32 + 1 × 16 + 1 × 8 + 0 × 4 + 1 × 2 + 1 × 1 = 1,691
Octal
3 2 3 3
3 × 512 + 2 × 64 + 3 × 8 + 3 × 1 = 1,691
Hexadecimal
6 9 b
6 × 256 + 9 × 16 + b × 1 = 1,691
Read as powers of two: 1,024 + 512 + 128 + 16 + 8 + 2 + 1 = 1,691.
In historical numeral systems
Egyptian
1 lotus, 6 coils of rope, 9 hobbles, 1 stroke
1 × 1,000 + 6 × 100 + 9 × 10 + 1 × 1 = 1,691. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
2 corner wedges + 8 vertical wedges (sixties place), 1 corner wedge + 1 vertical wedge (units place)
28 × 60 + 11 = 1691. 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
- Semiprime
Related numbers & connections
1691 is a year in the 17th century, in the 1690s.
Numbers Around Us
- appears inHistorical years
why?
Strength 0.50, confidence "high".
History
In 1691, the Treaty of Limerick ended the Williamite War in Ireland (Ireland).
DocumentedHistoryGeography: IrelandPeriod: 1691
Common questions
Is 1691 a prime number?
No, 1691 is not prime.
What are the factors of 1691?
The factors of 1691 are 1, 19, 89, 1691.
What is 1691 in Roman numerals?
1691 in Roman numerals is MDCXCI. XC is subtractive: ten before a hundred — a hundred minus ten. Written additively it would be MDCLXXXXI, which Roman inscriptions used freely — the strict subtractive form is a later convention.
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: 15 July 2026