From Wikipedia, the free encyclopedia
Natural 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
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)
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:
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
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