280
280 is a composite number, even, a calendar year.
280 (two hundred eighty) is an even 3-digit number. It is a composite number with 16 divisors, and factors as 2³ × 5 × 7. Its proper divisors sum to 440, more than the number itself, making it an abundant number. Written other ways, in Roman numerals it is CCLXXX and in binary, 100011000.
Interestingness
Historical context — 280 AD
Calendar year
Year 280 (CCLXXX) was a leap year starting on Thursday of the Julian calendar.
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Historical context — 280 BC
Calendar year
Year 280 BC was a year of the pre-Julian Roman calendar.
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Year facts
- Year type
-
Leap year
Divisible by 4 and not by 100; February has 29 days.
- Days in year
- 366
- ISO weeks
-
53
Long year: contains 53 ISO weeks.
- Started on
-
Thursday
January 1, 280
- Ended on
-
Friday
December 31, 280
- Friday the 13ths
-
2
2 Friday the 13ths this year.
- Decade
-
280s
280–289
- Century
-
3rd century
201–300
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,746
1746 years before 2026.
In other calendars
- Hebrew
-
4040 / 4041 AM
Rosh Hashanah falls in September/October.
- Chinese
-
Year of the zodiac:Metal zodiac:Rat
Sexagenary cycle position 37 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
823 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Ethiopian
-
272 / 273 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
202 / 201 Saka
Indian national calendar; year starts in March.
Properties
Primality
Prime factorization: 2 3 × 5 × 7
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√280 = [16; (1, 2, 1, 2, 1, 32)]
Period length 6 — the block in parentheses repeats forever.
Representations
- In words
- two hundred eighty
- Ordinal
- 280th
- Roman numeral
- CCLXXX
- Binary
- 100011000
- Octal
- 430
- Hexadecimal
- 0x118
- Base64
- ARg=
- One's complement
- 65,255 (16-bit)
- Scientific notation
- 2.8 × 10²
- As a duration
- 280 s = 4 minutes, 40 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒁹𒁹𒁹𒁹 𒌋𒌋𒌋𒌋
- Egyptian hieroglyphic
- 𓍢𓍢𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆
- Greek (Milesian)
- σπʹ
- Mayan (base 20)
- 𝋮·𝋠
- Chinese
- 二百八十
- Chinese (financial)
- 貳佰捌拾
Digit at this position in famous constants
- π — Pi (π)
- Digit 280 = 8
- e — Euler's number (e)
- Digit 280 = 2
- φ — Golden ratio (φ)
- Digit 280 = 7
- √2 — Pythagoras's (√2)
- Digit 280 = 9
- ln 2 — Natural log of 2
- Digit 280 = 4
- γ — Euler-Mascheroni (γ)
- Digit 280 = 6
Also seen as
Goldbach's conjecture says every even integer greater than 2 is the sum of two primes. For 280, here are decompositions:
- 3 + 277 = 280
- 11 + 269 = 280
- 17 + 263 = 280
- 23 + 257 = 280
- 29 + 251 = 280
- 41 + 239 = 280
- 47 + 233 = 280
- 53 + 227 = 280
Showing the first eight; more decompositions exist.
UTF-8 encoding: C4 98 (2 bytes).
As an unsigned 32-bit integer, this is the IPv4 address 0.0.1.24.
- Address
- 0.0.1.24
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.1.24
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Heard as a frequency, 280 Hz is closest to:
- Concert pitch (A4 = 440 Hz): C♯4 (277.2 Hz, +18¢)
- Scientific pitch (C4 = 256 Hz): D4 (287.4 Hz, -45¢ — about midway to C♯4)
- Baroque pitch (A4 = 415 Hz): D4 (277 Hz, +19¢)
On an ingredients label, E280 is Propionic acid, a preservative — which keeps bread from going mouldy.
Related reading
- Egyptian hieroglyphic numerals — Seven hieroglyphs for every power of ten, from a single stroke to a million.