ten

Ten is the natural number that follows nine and precedes eleven. It is the first two-digit number and the base of the decimal numeral system, used to count, measure, and perform arithmetic in most of the world.

In mathematics, ten is a composite number with divisors 1, 2, 5, and 10, and it equals 2×5. It is the sum 1+2+3+4, making it a triangular number. In numeral systems, ten is represented as X in Roman numerals, 1010 in binary, and A in hexadecimal.

The word ten derives from the Latin decem, via Old French dix and earlier languages; related prefixes include deka-, deca-, and the SI prefix deca (symbol da) for 10^1. The decimal system itself is named from this base-10 counting.

Culturally, ten appears in phrases such as a decade (a period of ten years) and a ten-sided polygon called a decagon. In science and measurement, decimal fractions, the decimal point, and the use of base-10 arithmetic underpin many systems of calculation and data representation, including counting scores, rates, and percentages.