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

← 79 81 → 80
← 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)
Numeral system	80
Factorization
Divisors	1, 2, 4, 5, 8, 10, 16, 20, 40, 80
Roman numeral	LXXX
Binary	10100002
Octal	1208
Duodecimal	6812
Hexadecimal	5016

In mathematics

The sum of Euler's totient function φ(x) over the first sixteen integers is 80.

Adding up some subsets of its divisors (e.g., 1, 4, 5, 10, 20 and 40) gives 80, hence 80 is a semiperfect number.

80 is a ménage number, and is a Harshad number number in base 10.

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.^[1][2]

In science

Element 80: Mercury (Hg)

• The atomic number of mercury
• A rectifier vacuum tube manufactured from the mid-1920s through the mid-1980s, the longest production run of any American vacuum tube.^{[citation needed]}

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 sports

Jerry Rice wore the number 80 for the majority of his NFL career. The number 80 is also the retired number of Seattle Seahawks wide receiver Steve Largent; when Rice was traded to the Seahawks, Largent gave the team permission to unretire his number so Rice could wear it.

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
• I-80 is an interstate highway going from New York to San Francisco
• 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

References

1. ^ Bunkley, Nick (March 3, 2008), "Joseph Juran, 103, Pioneer in Quality Control, Dies", New York Times, http://www.nytimes.com/2008/03/03/business/03juran.html .
2. ^ What is 80/20 Rule, Pareto’s Law, Pareto Principle, http://www.80-20presentationrule.com/whatisrule.html .

External links

Wikimedia Commons has media related to: 80 (number)

• wiktionary:eighty for 80 in other languages.