1781
1781 is the year Uranus was discovered.
- Odd
- Composite
Where 1781 fits
Why 1781 is special
It was the first planet found with a telescope rather than known since antiquity, and it doubled the known size of the solar system overnight. Herschel initially reported it as a comet and wanted to name it after King George III.
Factors & digit properties
- Divisors (4)
- 1, 13, 137, 1781
- Prime factorisation
- 13 × 137
- Digit sum
- 17
- Digital root
- 8
Representations
- Decimal
- 1781
- Binary
- 11011110101
- Octal
- 3365
- Hexadecimal
- 6f5
- Roman numeral
- MDCCLXXXI
- Scientific notation
- 1.781 × 10^3
Other mathematical patterns
- Deficient number
- Semiprime
Related numbers & connections
Newtonian gravitation is what let astronomers infer an unseen planet from orbital irregularities — the method that found Uranus's successor and confirmed the theory that predicted it.
View 1687 →Other connections
- is associated with1687
why?
Strength 0.50, confidence "high".
Science
Uranus was the first planet found with a telescope rather than known since antiquity, and its discovery doubled the known extent of the solar system. Herschel first reported it as a comet and proposed naming it after George III.
DocumentedSciencePeriod: 1781
Common questions
Is 1781 a prime number?
No, 1781 is not prime.
What are the factors of 1781?
The factors of 1781 are 1, 13, 137, 1781.
What is 1781 in Roman numerals?
1781 in Roman numerals is MDCCLXXXI.
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: 3 August 2026