Negative numbers, zero, and one are neither prime nor composite. See the related questions as to an explanation why.
See whether the number is divisible by 2, and by all odd numbers up to the square root of the number. For numbers up to 100, it is enough to check the factors 2, 3, 5, and 7. For higher numbers you need to check more factors.
For very large numbers (for example, hundreds of digits), more efficient methods are known, but those methods are also more complicated.
Check the related link for a number factoring calculator.
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Prime numbers have two factors, composite numbers have more than two.
The answer depends on whether or not the prime number is a factor of the other number.If the prime number is a factor of the other number then the GCF is the prime, otherwise the GCF is 1.
It is prime
86 is not a prime number, so is a composite.
No 168 is not a prime number it is a composite number