Are all even numbers composite?

Not all even numbers are composite—specifically, 2 is an even number but it's prime, not composite. The number 2 is the only even prime number because it has exactly two factors: 1 and 2. Every other even number greater than 2 (4, 6, 8, 10, 12, etc.) is composite because it's divisible by 2, which means these numbers automatically have more than two factors: 1, 2, at least one other factor, and the number itself.

This exception makes 2 unique in number theory as the only even prime, a fact that has practical implications for mathematical proofs and algorithms. When programming divisibility tests or prime-checking functions, developers typically handle 2 as a special case before checking odd numbers, since testing even numbers beyond 2 for primality is unnecessary—they're guaranteed to be composite. In cryptography and security applications, this property means even numbers (except 2) are never used as prime factors in encryption keys. For students learning factorization, recognizing that "even means composite" works as a reliable rule with exactly one exception creates a powerful mental shortcut. This pattern also explains why prime numbers greater than 2 must be odd, since being even would automatically make them divisible by 2 and therefore composite.