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.
Read more about this topic: 80 (number)
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