80 (number)

80 is the natural number following 79 and preceding 81.

In mathematics

80 is:

The sum of Euler's totient function φ over the first sixteen integers:
A semiperfect number, since adding up some subsets of its divisors gives 80.
A ménage number.
Palindromic in bases 3, 6, 9, 15, 19, and 39.
A repdigit in bases 3, 9, 15, 19, and 39.
The sum of the first four twin prime pairs:

The Pareto principle states that, for many events, roughly 80% of the effects come from 20% of the causes.
Every solvable configuration of the 15 puzzle can be solved in no more than 80 single-tile moves.