80
80 is a composite number, even, a calendar year.
80 (eighty) is an even 2-digit number. It is a composite number with 10 divisors, and factors as 2⁴ × 5. Its proper divisors sum to 106, more than the number itself, making it an abundant number. Written other ways, in Roman numerals it is LXXX and in binary, 1010000.
Interestingness
Historical context — 80 AD
Calendar year
AD 80 (LXXX) was a leap year starting on Saturday of the Julian calendar.
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Historical context — 80 BC
Calendar year
Year 80 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
- 52
- Started on
-
Monday
January 1, 80
- Ended on
-
Tuesday
December 31, 80
- Friday the 13ths
-
2
2 Friday the 13ths this year.
- Decade
-
80s
80–89
- Century
-
1st century
1–100
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,946
1946 years before 2026.
In other calendars
- Hebrew
-
3840 / 3841 AM
Rosh Hashanah falls in September/October.
- Chinese
-
Year of the zodiac:Metal zodiac:Dragon
Sexagenary cycle position 17 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
623 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Ethiopian
-
72 / 73 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
2 / 1 Saka
Indian national calendar; year starts in March.
Properties
Primality
Prime factorization: 2 4 × 5
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√80 = [8; (1, 16)]
Period length 2 — the block in parentheses repeats forever.
Representations
- In words
- eighty
- Ordinal
- 80th
- Roman numeral
- LXXX
- Binary
- 1010000
- Octal
- 120
- Hexadecimal
- 0x50
- Base64
- UA==
- One's complement
- 175 (8-bit)
- Scientific notation
- 8 × 10¹
- As a duration
- 80 s = 1 minute, 20 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒁹 𒌋𒌋
- Egyptian hieroglyphic
- 𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆
- Greek (Milesian)
- πʹ
- Mayan (base 20)
- 𝋤·𝋠
- Chinese
- 八十
- Chinese (financial)
- 捌拾
Digit at this position in famous constants
- π — Pi (π)
- Digit 80 = 9
- e — Euler's number (e)
- Digit 80 = 5
- φ — Golden ratio (φ)
- Digit 80 = 4
- √2 — Pythagoras's (√2)
- Digit 80 = 0
- ln 2 — Natural log of 2
- Digit 80 = 7
- γ — Euler-Mascheroni (γ)
- Digit 80 = 6
Also seen as
Goldbach's conjecture says every even integer greater than 2 is the sum of two primes. For 80, here are decompositions:
- 7 + 73 = 80
- 13 + 67 = 80
- 19 + 61 = 80
- 37 + 43 = 80
As an ASCII codepoint, 80 is P. Printable ASCII character P.
TCP/UDP port 80 is the well-known port for HTTP — HyperText Transfer Protocol — the web.
As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.80.
- Address
- 0.0.0.80
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.0.80
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Matches numbered highway designation:
- I-80 — San Francisco, CA to Teaneck, NJ — the longest northern coast-to-coast.
Heard as a frequency, 80 Hz is closest to:
- Concert pitch (A4 = 440 Hz): D♯2 (77.8 Hz, +49¢ — about midway to E2)
- Scientific pitch (C4 = 256 Hz): E2 (80.6 Hz, -14¢)
- Baroque pitch (A4 = 415 Hz): E2 (77.7 Hz, +50¢ — about midway to F2)
As a MIDI note number, 80 is G♯5 (830.6 Hz at concert pitch).
On the periodic table, atomic number 80 is Mercury (Hg) — period 6.
Related reading
- Mayan numerals — Vigesimal dots-and-bars with a shell zero — one of the earliest true zeros.