491
K. 491 is the C minor piano concerto.
- Odd
- Prime
Where 491 fits
Why 491 is special
It uses the largest orchestra of any Mozart concerto, including both oboes and clarinets, which is a combination he otherwise avoided.
491 is part of
Factors & digit properties
- Divisors (2)
- 1, 491
- Prime factorisation
- 491
- Digit sum
- 14
- Digital root
- 5
Representations
- Decimal
- 491
- Scientific notation
- 4.910 × 10^2
Roman numerals
C D X C I
CDXCI uses the subtractive pair XC: ten before a hundred — a hundred minus ten.
Binary
1 1 1 1 0 1 0 1 1
1 × 256 + 1 × 128 + 1 × 64 + 1 × 32 + 0 × 16 + 1 × 8 + 0 × 4 + 1 × 2 + 1 × 1 = 491
Octal
7 5 3
7 × 64 + 5 × 8 + 3 × 1 = 491
Hexadecimal
1 e b
1 × 256 + e × 16 + b × 1 = 491
Read as powers of two: 256 + 128 + 64 + 32 + 8 + 2 + 1 = 491.
In historical numeral systems
Egyptian
4 coils of rope, 9 hobbles, 1 stroke
4 × 100 + 9 × 10 + 1 × 1 = 491. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
8 vertical wedges (sixties place), 1 corner wedge + 1 vertical wedge (units place)
8 × 60 + 11 = 491. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
upsilon, then koppa, then alpha, marked as a numeral
upsilon-koppa-alpha + keraia
upsilon + koppa + alpha written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
tav, then tsadi, then alef
tav-tsadi-alef
tav (400) + tsadi (90) + alef (1) = 491, written in descending order.
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
- Sophie Germain prime
Related numbers & connections
Mozart's two minor-key piano concertos, one with Beethoven's cadenzas and one with his largest orchestra.
View 466 →The pair are routinely programmed together as the minor-key concertos.
View 466 →Media & popular culture
K. 491 employs Mozart's largest concerto orchestra, uniquely including both oboes and clarinets alongside flute, bassoons, horns, trumpets and timpani.
DocumentedMedia & popular cultureGeography: AustriaPeriod: 1786
Common questions
Is 491 a prime number?
Yes, 491 is prime — it has exactly two positive divisors: 1 and itself.
What are the factors of 491?
The factors of 491 are 1, 491.
What is 491 in Roman numerals?
491 in Roman numerals is CDXCI. XC is subtractive: ten before a hundred — a hundred minus ten. Written additively it would be CCCCLXXXXI, 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