80 (number)

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

In mathematics

80 is:

• the sum of Euler's totient function φ(x) over the first sixteen integers.
• a
  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

• 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
  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
  port number for HTTP
  connections
• the 80A, 80B and 80C
  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
  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

External links

Wikimedia Commons has media related to 80 (number).

• wiktionary:eighty for 80 in other languages.