composite number
A composite number is a positive integer which is not prime and not equal to 1. That is, is composite if , with and natural numbers both not equal to 1.
Examples.
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1 is not composite (and also not prime), by definition.
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2 is not composite, as it is prime.
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15 is composite, since .
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93555 is composite, since .
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52223 is not composite, since it is prime.
More generally, we can define compositeness any time there is an ambient notion of an irreducible element. In an integral domain
, for example, an element is said to be composite if it neither zero, a unit, nor irreducible.