891
NGC 891 is the edge-on spiral with visible dust filaments.
- Odd
- Composite
Where 891 fits
Why 891 is special
Deep images show dust extending vertically out of the disc, lifted by star formation, which is the process that seeds the halo with heavy elements.
Factors & digit properties
- Divisors (10)
- 1, 3, 9, 11, 27, 33, 81, 99, 297, 891
- Prime factorisation
- 3^4 × 11
- Digit sum
- 18
- Digital root
- 9
Representations
- Decimal
- 891
- Scientific notation
- 8.910 × 10^2
Roman numerals
D C C C X C I
DCCCXCI uses the subtractive pair XC: ten before a hundred — a hundred minus ten.
Binary
1 1 0 1 1 1 1 0 1 1
1 × 512 + 1 × 256 + 0 × 128 + 1 × 64 + 1 × 32 + 1 × 16 + 1 × 8 + 0 × 4 + 1 × 2 + 1 × 1 = 891
Octal
1 5 7 3
1 × 512 + 5 × 64 + 7 × 8 + 3 × 1 = 891
Hexadecimal
3 7 b
3 × 256 + 7 × 16 + b × 1 = 891
Read as powers of two: 512 + 256 + 64 + 32 + 16 + 8 + 2 + 1 = 891.
In historical numeral systems
Egyptian
8 coils of rope, 9 hobbles, 1 stroke
8 × 100 + 9 × 10 + 1 × 1 = 891. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
1 corner wedge + 4 vertical wedges (sixties place), 5 corner wedges + 1 vertical wedge (units place)
14 × 60 + 51 = 891. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
omega, then koppa, then alpha, marked as a numeral
omega-koppa-alpha + keraia
omega + 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 tav, then tsadi, then alef
tav-tav-tsadi-alef
tav (400) + tav (400) + tsadi (90) + alef (1) = 891, 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
Related numbers & connections
Both are edge-on spirals showing material lifted vertically out of the disc by star formation.
View 4631 →Science
NGC 891 is an edge-on spiral showing filamentary dust extending perpendicular to the plane, associated with supernova-driven outflow from the disc.
DocumentedSciencePeriod: 1784–
Common questions
Is 891 a prime number?
No, 891 is not prime.
What are the factors of 891?
The factors of 891 are 1, 3, 9, 11, 27, 33, 81, 99, 297, 891.
What is 891 in Roman numerals?
891 in Roman numerals is DCCCXCI. XC is subtractive: ten before a hundred — a hundred minus ten. Written additively it would be DCCCLXXXXI, 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