251
+251 is the international calling code for Ethiopia.
- Odd
- Prime
Where 251 fits
Why 251 is special
Ethiopia uses its own calendar, which runs seven to eight years behind the Gregorian one and has thirteen months. A country's telephone code is ordinary; its calendar is one of the few national ones still in everyday official use.
251 is part of
Factors & digit properties
- Divisors (2)
- 1, 251
- Prime factorisation
- 251
- Digit sum
- 8
- Digital root
- 8
Representations
- Decimal
- 251
- Scientific notation
- 2.510 × 10^2
Roman numerals
C C L I
Binary
1 1 1 1 1 0 1 1
1 × 128 + 1 × 64 + 1 × 32 + 1 × 16 + 1 × 8 + 0 × 4 + 1 × 2 + 1 × 1 = 251
Octal
3 7 3
3 × 64 + 7 × 8 + 3 × 1 = 251
Hexadecimal
f b
f × 16 + b × 1 = 251
Read as powers of two: 128 + 64 + 32 + 16 + 8 + 2 + 1 = 251.
In historical numeral systems
Egyptian
2 coils of rope, 5 hobbles, 1 stroke
2 × 100 + 5 × 10 + 1 × 1 = 251. 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), 1 corner wedge + 1 vertical wedge (units place)
4 × 60 + 11 = 251. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
sigma, then nu, then alpha, marked as a numeral
sigma-nu-alpha + keraia
sigma + nu + 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 nun, then alef
resh-nun-alef
resh (200) + nun (50) + alef (1) = 251, written in descending order.
Maya
2 bars + 2 dots (upper, twenties place) over 2 bars + 1 dot (lower, units place)
12 × 20 + 11 = 251. 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
Related numbers & connections
Eritrea separated from Ethiopia in 1993 after a thirty-year war. Eritrea has among the lowest internet penetration in the world, which is state policy rather than infrastructure.
View 291 →Geography
+251 reaches Ethiopia, in the 2x block covering Africa. Ethiopia is also one of very few countries running its own calendar in official daily use, currently seven to eight years behind the Gregorian year.
DocumentedGeographyGeography: Ethiopia
Common questions
Is 251 a prime number?
Yes, 251 is prime — it has exactly two positive divisors: 1 and itself.
What are the factors of 251?
The factors of 251 are 1, 251.
What is 251 in Roman numerals?
251 in Roman numerals is CCLI.
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