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Cardinal | eighty | |||

Ordinal | 80th (eightieth) | |||

Factorization | 2^{4}× 5 | |||

Divisors | 1, 2, 4, 5, 8, 10, 16, 20, 40, 80 | |||

Greek numeral | Π´ | |||

Roman numeral | LXXX | |||

Binary | 1010000_{2} | |||

Ternary | 2222_{3} | |||

Quaternary | 1100_{4} | |||

Quinary | 310_{5} | |||

Senary | 212_{6} | |||

Octal | 120_{8} | |||

Duodecimal | 68_{12} | |||

Hexadecimal | 50_{16} | |||

Vigesimal | 40_{20} | |||

Base 36 | 28_{36} |

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

## Contents

## 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 (2222
_{3}), 6 (212_{6}), 9 (88_{9}), 15 (55_{15}), 19 (44_{19}) and 39 (22_{39}). - a repdigit in bases 3, 9, 15, 19 and 39.

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 Fifteen puzzle can be solved in no more than 80 single-tile moves.^{[5]}

## In science

- 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*

## See also

## References

**^**"Sloane's A005835 : Pseudoperfect (or semiperfect) numbers".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2016-05-29.**^**"Sloane's A000179 : Ménage numbers".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2016-05-29.**^**Bunkley, Nick (March 3, 2008). "Joseph Juran, 103, Pioneer in Quality Control, Dies".*The New York Times*..**^**"What is 80/20 Rule, Pareto's Law, Pareto Principle". Archived from the original on 2013-01-28. Retrieved 2017-05-20..**^**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

Wikimedia Commons has media related to .80 (number) |

- wiktionary:eighty for
*80*in other languages.