80 (number)

80 (eighty) is the natural number following 79 and preceding 81.

← 79 80 81 →
← 80 81 82 83 84 85 86 87 88 89 → List of numbers Integers ← 0 10 20 30 40 50 60 70 80 90 →
Cardinal	eighty
Ordinal	80th (eightieth)
Factorization	24 × 5
Divisors	1, 2, 4, 5, 8, 10, 16, 20, 40, 80
Greek numeral	Π´
Roman numeral	LXXX
Binary	10100002
Ternary	22223
Senary	2126
Octal	1208
Duodecimal	6812
Hexadecimal	5016
Armenian	Ձ
Hebrew	פ / ף
Babylonian numeral	𒐕⟪
Egyptian hieroglyph	𓎍

In mathematics

80 is:

• the sum of Euler's totient function φ(x) over the first sixteen integers.
• a semiperfect number, since adding up some subsets of its divisors (e.g., 1, 4, 5, 10, 20 and 40) gives 80.^[1]
• a ménage number.^[2]
• palindromic in bases 3 (2222₃), 6 (212₆), 9 (88₉), 15 (55₁₅), 19 (44₁₉) and 39 (22₃₉).
• a repdigit in bases 3, 9, 15, 19 and 39.
• the sum of the first 4 twin prime pairs ((3 + 5) + (5 + 7) + (11 + 13) + (17 + 19)).

The Pareto principle (also known as the 80-20 rule) states that, for many events, roughly 80% of the effects come from 20% of the causes.^[3][4]

Every solvable configuration of the 15 puzzle can be solved in no more than 80 single-tile moves.^[5]

In science

Element 80: Mercury (Hg)

• The atomic number of mercury

In religion

• According to Exodus 7:7, Moses was 80 years old when he initially spoke to Pharaoh on behalf of his people. Today, 80 years of age is the upper age limit for cardinals to vote in papal elections.

In other fields

Eighty is also:

• used in the classic book title Around the World in Eighty Days
• the length of the Eighty Years' War or Dutch revolt (1568–1648)
• the standard TCP/IP port number for HTTP connections
• the 80A, 80B and 80C photographic filters correct for excessive redness under tungsten lighting
• The year AD 80, 80 BC, or 1980
• Eighty shilling ale
• The older four-pin-base version of the 5Y3GT rectifier tube
• A common limit for the characters per line, in computing, derived from the number of columns in IBM cards
• American band Green Day has a song called "80"
• A fictional alien superhero named Ultraman 80
• On the Réaumur scale, 80 degrees is the boiling temperature of pure water at sea level

See also

• List of highways numbered 80

References

1. "Sloane's A005835 : Pseudoperfect (or semiperfect) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
2. "Sloane's A000179 : Ménage numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
3. Bunkley, Nick (March 3, 2008). "Joseph Juran, 103, Pioneer in Quality Control, Dies". The New York Times..
4. "What is 80/20 Rule, Pareto's Law, Pareto Principle". Archived from the original on 2013-01-28. Retrieved 2017-05-20..
5. A. Brüngger, A. Marzetta, K. Fukuda and J. Nievergelt, The parallel search bench ZRAM and its applications, Annals of Operations Research 90 (1999), pp. 45–63.

External links

• wiktionary:eighty for 80 in other languages.