281
NGC 281 is the Pacman Nebula.
- Odd
- Prime
Where 281 fits
Why 281 is special
Its dark lane produces the resemblance, and the informal name is now used in professional literature, which is unusual for a nickname of that origin.
Same number, different meanings
How 281 is understood across different contexts — never implying one meaning because of another.
- Mathematics
Its dark lane produces the resemblance, and the informal name is now used in professional literature, which is unusual for a nickname of that origin.
- Technology & computing
There are about 281 trillion possible MAC addresses (worldwide, network hardware addressing). Exactly 2⁴⁸. Half are reserved by convention, and the first three bytes identify the manufacturer, so the usable space per vendor is far smaller than the total suggests.
- Science
NGC 281 is an emission nebula in Cassiopeia whose foreground dust lane produces its common name, now used alongside the catalogue designation.
281 is part of
Factors & digit properties
- Divisors (2)
- 1, 281
- Prime factorisation
- 281
- Digit sum
- 11
- Digital root
- 2
Representations
- Decimal
- 281
- Scientific notation
- 2.810 × 10^2
Roman numerals
C C L X X X I
Binary
1 0 0 0 1 1 0 0 1
1 × 256 + 0 × 128 + 0 × 64 + 0 × 32 + 1 × 16 + 1 × 8 + 0 × 4 + 0 × 2 + 1 × 1 = 281
Octal
4 3 1
4 × 64 + 3 × 8 + 1 × 1 = 281
Hexadecimal
1 1 9
1 × 256 + 1 × 16 + 9 × 1 = 281
Read as powers of two: 256 + 16 + 8 + 1 = 281.
In historical numeral systems
Egyptian
2 coils of rope, 8 hobbles, 1 stroke
2 × 100 + 8 × 10 + 1 × 1 = 281. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
4 vertical wedges (sixties place), 4 corner wedges + 1 vertical wedge (units place)
4 × 60 + 41 = 281. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
sigma, then pi, then alpha, marked as a numeral
sigma-pi-alpha + keraia
sigma + pi + alpha written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
resh, then pe, then alef
resh-pe-alef
resh (200) + pe (80) + alef (1) = 281, written in descending order.
Maya
2 bars + 4 dots (upper, twenties place) over 1 dot (lower, units place)
14 × 20 + 1 = 281. Places stack vertically with the smallest at the bottom, so the upper group is worth twenty times the lower.
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
- Twin prime
Related numbers & connections
Both are emission nebulae with young clusters whose radiation will disperse them within a few million years.
View 7380 →Other connections
- is associated with7380
why?
Strength 0.50, confidence "high".
Technology & computing
There are about 281 trillion possible MAC addresses (worldwide, network hardware addressing). Exactly 2⁴⁸. Half are reserved by convention, and the first three bytes identify the manufacturer, so the usable space per vendor is far smaller than the total suggests.
DocumentedTechnology & computingGeography: worldwide, network hardware addressing
Science
NGC 281 is an emission nebula in Cassiopeia whose foreground dust lane produces its common name, now used alongside the catalogue designation.
DocumentedSciencePeriod: 1883–
Common questions
Is 281 a prime number?
Yes, 281 is prime — it has exactly two positive divisors: 1 and itself.
What are the factors of 281?
The factors of 281 are 1, 281.
What is 281 in Roman numerals?
281 in Roman numerals is CCLXXXI.
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