80 (number)
(Redirected from Number 80)
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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]
References
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- ↑ 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
- wiktionary:eighty for 80 in other languages.