composite number

Also known as: nonprime number

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July 23, 2026

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A composite number is a whole number greater than 1 that has more than two factors. This means it can be divided evenly by numbers other than 1 and itself. For example, 4 is a composite number because it can be divided by 1, 2, and 4. In contrast, a prime number has only two factors: 1 and itself.1

The concept of composite numbers is fundamental to number theory. The fundamental theorem of arithmetic states that every whole number greater than 1 can be uniquely expressed as a product of its prime factors. Factoring large composite numbers is crucial in modern cryptography for securing information online.1

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$A page from a first-grade workbook typical of “new math” might state: “Draw connecting lines from triangles in the first set to triangles in the second set. Are the two sets equivalent in number?”$
arithmetic
Fundamental theory
…1, then c is called composite. A positive integer neither 1 nor composite is called a prime number. Thus, 2, 3, 5, 7, 11, 13, 17, 19, … are prime numbers. The ancient Greek mathematician Euclid proved in his Elements (c. 300 bc) that there are infinitely many prime numbers.
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…1, then c is called composite. A positive integer neither 1 nor composite is called a prime number. Thus, 2, 3, 5, 7, 11, 13, 17, 19, … are prime numbers. The ancient Greek mathematician Euclid proved in his Elements (c. 300 bc) that there are infinitely many prime numbers.
Read More

factor
…than two factors is called composite. The prime factors of a number or expression are simply the factors that are prime. According to the fundamental theorem of arithmetic, every whole number greater than 1 can be written as a product of its prime factors in a way that is unique,…
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…than two factors is called composite. The prime factors of a number or expression are simply the factors that are prime. According to the fundamental theorem of arithmetic, every whole number greater than 1 can be written as a product of its prime factors in a way that is unique,…
Read More