4th grade Math: How to find out if a large number is prime number or composite?

Question

Need to know how a 4th grader can tell if a large number (over 3 digits long) is a prime number.  Is there a formula or helpful trick (other than division)?

Answer 1

Prime numbers can only be factored by itsself and 1.

Composiste numbers can be factored by itssefl one and at least one more number.

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