10 (number)

Ten (10) is a natural number that comes after 9 and before 11. It is an even number divisible by 1, 2, 5, and 10. It is therefore not a prime number, but rather the product of two primes: 2 and 5.

Ten is significant as the base of the decimal numeral system, the standard way numbers are written today. In this system, each position in a number represents a power of 10: 1, 10, 100, 1000, and so on. This system is thought to derive from counting on the ten fingers of both hands.

Mathematical properties

Ten is the third triangular number (after 1 and 3 and 6), being the sum 1+2+3+4. It is also the sum of the first four numbers. The divisors of ten are 1, 2, 5, and 10, which sum to 18. In binary notation, ten is written as 1010.

Notation and symbols

In the Hindu-Arabic numeral system, ten is written with two symbols: 1 and 0. In Roman numerals it is written as X. In Somali, the number is called toban, and the numbers 11 through 19 are formed by compounds based on ten (ten and one, ten and two, and so forth).

Use in measurements

The metric system of measurement operates on powers of ten: the metre, the kilometre (1000 metres), the centimetre (one hundredth of a metre). Likewise percentages and parts per hundred are based on powers of ten. Logarithms with base ten (log₁₀) are used in measurements such as the Richter scale and decibels.

Cultural and other references

Ten is commonly used for rankings and divisions: top-ten lists and groups of ten units. Various cultures and traditions use the number ten in ranking systems or divisions.