1668
1668 is the year Newton built the first practical reflecting telescope.
- Even
- Composite
Where 1668 fits
Why 1668 is special
Mirrors avoid the colour fringing that lenses produce. Almost every large telescope since, including Hubble and Webb, is a reflector.
Factors & digit properties
- Divisors (12)
- 1, 2, 3, 4, 6, 12, 139, 278, 417, 556, 834, 1668
- Prime factorisation
- 2^2 × 3 × 139
- Digit sum
- 21
- Digital root
- 3
Representations
- Decimal
- 1668
- Binary
- 11010000100
- Octal
- 3204
- Hexadecimal
- 684
- Roman numeral
- MDCLXVIII
- Scientific notation
- 1.668 × 10^3
Other mathematical patterns
- Abundant number
Related numbers & connections
Portugal declared independence from Spain in 1640 and Spain recognised it in 1668 — a coup that took a day and a war that took twenty-eight years.
View 1640 →Technology & computing
Newton's 1668 reflector used a mirror rather than a lens, avoiding chromatic aberration and the impractical lengths refractors required. Every major telescope built since follows that choice.
DocumentedTechnology & computingGeography: EnglandPeriod: 1668Spain built its conventional railways to Iberian gauge and its high-speed lines to standard gauge, so it operates both. Some trains have variable-gauge axles that change while moving slowly through a trackside device.
DocumentedTechnology & computingGeography: Spain and Portugal
Common questions
Is 1668 a prime number?
No, 1668 is not prime.
What are the factors of 1668?
The factors of 1668 are 1, 2, 3, 4, 6, 12, 139, 278, 417, 556, 834, 1668.
What is 1668 in Roman numerals?
1668 in Roman numerals is MDCLXVIII.
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: 3 August 2026