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.
1781 is part of
Factors & digit properties
- Divisors (4)
- 1, 13, 137, 1781
- Prime factorisation
- 13 × 137
- Digit sum
- 17
- Digital root
- 8
Representations
- Decimal
- 1781
- Scientific notation
- 1.781 × 10^3
Roman numerals
M D C C L X X X I
Binary
1 1 0 1 1 1 1 0 1 0 1
1 × 1,024 + 1 × 512 + 0 × 256 + 1 × 128 + 1 × 64 + 1 × 32 + 1 × 16 + 0 × 8 + 1 × 4 + 0 × 2 + 1 × 1 = 1,781
Octal
3 3 6 5
3 × 512 + 3 × 64 + 6 × 8 + 5 × 1 = 1,781
Hexadecimal
6 f 5
6 × 256 + f × 16 + 5 × 1 = 1,781
Read as powers of two: 1,024 + 512 + 128 + 64 + 32 + 16 + 4 + 1 = 1,781.
In historical numeral systems
Egyptian
1 lotus, 7 coils of rope, 8 hobbles, 1 stroke
1 × 1,000 + 7 × 100 + 8 × 10 + 1 × 1 = 1,781. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
2 corner wedges + 9 vertical wedges (sixties place), 4 corner wedges + 1 vertical wedge (units place)
29 × 60 + 41 = 1781. 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
1781 is a year in the 18th century, in the 1780s.
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 →Numbers Around Us
- appears inHistorical years
why?
Strength 0.50, confidence "high".
Other connections
- is associated with1687
why?
Strength 0.50, confidence "high".
Science
In 1781, William Herschel discovered Uranus, the first planet found with a telescope (England).
DocumentedScienceGeography: EnglandPeriod: 1781Uranus 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: 2 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026