80 (number)
From Halbeeg, the open encyclopedia · Af-Soomaali
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80 is a natural number that comes after 79 and before 81. It is an even number, meaning it is divisible by two with no remainder.
In Roman numerals it is written as LXXX. In the Arabic-Hindu decimal system used worldwide, it is written with two digits: 8 and 0, representing three tens.
Mathematical properties
80 is a composite number, not a prime number. Its divisors are 1, 2, 4, 5, 8, 10, 16, 20, 40, and 80. Its prime factorization is 2⁴ × 5. It therefore has ten divisors in total.
80 lies between the perfect square 81 (9 × 9) and the prime number 79. It is also the product of 16 and 5, and of 8 and 10.
Use in language and measurement
In Somali, 80 is called "sideetan", derived from "siddeed" (three) and the tens place. In other languages such as French, 80 is expressed as "quatre-vingts" (four twenties), reflecting a counting system based on twenty.
Other contexts
80 as a percentage is commonly used as a general measure indicating a large portion of something. In chemistry, atomic number 80 corresponds to mercury. In history, the year 80 and the 80th century are part of calendar usage.