A composite number (or simply a composite) is a natural number, that can be found by multiplying prime numbers.

For example, the number 9 can be found by multiplying 3 by 3. Another example is the number 12, which is obtained by multiplying 3, 2 and 2.

All natural numbers (greater than 1) can be put in one of the two classes below:

• The number is prime.
• The number is not prime. It can be found by multiplying together other primes. The same prime number can be used several times, as in the example with 12 above. This is known as the fundamental theorem of arithmetic.

• Perfect number

v t e Divisibility-based sets of integers
Overview	Integer factorization Divisor Unitary divisor Divisor function Prime factor Fundamental theorem of arithmetic
Factorization forms	Prime Composite Semiprime Pronic Sphenic Square-free Powerful Perfect power Achilles Smooth Regular Rough Unusual
Constrained divisor sums	Perfect Almost perfect Quasiperfect Multiply perfect Hemiperfect Hyperperfect Superperfect Unitary perfect Semiperfect Practical Erdős–Nicolas
With many divisors	Abundant Primitive abundant Highly abundant Superabundant Colossally abundant Highly composite Superior highly composite Weird
Aliquot sequence-related	Untouchable Amicable (Triple) Sociable Betrothed
Base-dependent	Equidigital Extravagant Frugal Harshad Polydivisible Smith
Other sets	Arithmetic Deficient Friendly Solitary Sublime Harmonic divisor Descartes Refactorable Superperfect

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