# 80 (number)

 ← 79 80 81 →
Cardinal eighty
Ordinal 80th
(eightieth)
Factorization 24× 5
Divisors 1, 2, 4, 5, 8, 10, 16, 20, 40, 80
Roman numeral LXXX
Binary 10100002
Ternary 22223
Quaternary 11004
Quinary 3105
Senary 2126
Octal 1208
Duodecimal 6812
Vigesimal 4020
Base 36 2836
Hebrew פ (Peh)

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

## 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 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)

## 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.

Eighty is also:

## References

1. ^ Bunkley, Nick (March 3, 2008), Joseph Juran, 103, Pioneer in Quality Control, Dies, New York Times.
2. ^