A good way to instantly tell if a number is prime or composite is to learn some tricks to tell if a number divides by certain numbers. For instance, if a number is even, we know it is composite as it must be divisible by 2. If a number ends in 0 or 5, then it also cannot be prime as it would be divisible by 5. In this case, the number ends in 5, so we can tell it must be composite and cannot be prime.
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4, composite. 67, prime.
Prime
1 is special 2 prime 3 prime 4 composite 5 prime 6 composite 7 prime 8 composite 9 composite 10 composite 11 prime 12 composite ext.
5 prime, 25 composite.
Composite