Take a prime number for example 7. You can break a prime number like that into 2 or more parts as long as they are unequal. So I can break 7 into 2 and a 5. or 3 and a 4. But those are not equal parts.

There is no way to break 7 into equal parts like you can do for 15. For 15 I can break it up into 5 equal parts with 3 each. But I can not do that for 7.

So a prime number by definition can not be broken down into equal parts