280
Human pregnancy is conventionally counted as 280 days.
- Even
- Composite
Where 280 fits
Why 280 is special
It is measured from the last menstrual period rather than conception, so the count begins about two weeks before the pregnancy does. Roughly four percent of births occur on the estimated date.
280 is part of
Factors & digit properties
- Divisors (16)
- 1, 2, 4, 5, 7, 8, 10, 14, 20, 28, 35, 40, 56, 70, 140, 280
- Prime factorisation
- 2^3 × 5 × 7
- Digit sum
- 10
- Digital root
- 1
Representations
- Decimal
- 280
- Scientific notation
- 2.800 × 10^2
Roman numerals
C C L X X X
Binary
1 0 0 0 1 1 0 0 0
1 × 256 + 0 × 128 + 0 × 64 + 0 × 32 + 1 × 16 + 1 × 8 + 0 × 4 + 0 × 2 + 0 × 1 = 280
Octal
4 3 0
4 × 64 + 3 × 8 + 0 × 1 = 280
Hexadecimal
1 1 8
1 × 256 + 1 × 16 + 8 × 1 = 280
Read as powers of two: 256 + 16 + 8 = 280.
In historical numeral systems
Egyptian
2 coils of rope, 8 hobbles
2 × 100 + 8 × 10 = 280. 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 (units place)
4 × 60 + 40 = 280. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
sigma, then pi, marked as a numeral
sigma-pi + keraia
sigma + pi 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
resh-pe
resh (200) + pe (80) = 280, written in descending order.
Maya
2 bars + 4 dots (upper, twenties place) over shell (zero) (lower, units place)
14 × 20 + 0 = 280. 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
- Abundant number
- Happy number
- Harshad (Niven) number
Science
The 280-day figure runs from the last menstrual period, not from conception, which means the first fortnight of a pregnancy predates the pregnancy. Only about one birth in twenty-five falls on the calculated date.
DocumentedScience
Common questions
Is 280 a prime number?
No, 280 is not prime.
What are the factors of 280?
The factors of 280 are 1, 2, 4, 5, 7, 8, 10, 14, 20, 28, 35, 40, 56, 70, 140, 280.
What is 280 in Roman numerals?
280 in Roman numerals is CCLXXX.
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