The task in the image is to sort numbers into the categories Prime, Composite, or Neither. The number 21 at the bottom needs to be categorized correctly. Here's the solution:

• 21 is Composite, as it can be divided by 1, 3, 7, and 21 (more than two factors).

Would you like an explanation about how to determine whether a number is prime, composite, or neither? Let me know if you have more questions or want further examples.

Follow-up Questions:

1. What are the properties of a prime number?
2. How can we determine if a number is composite?
3. Why is 1 considered "neither" prime nor composite?
4. What are examples of prime numbers between 1 and 20?
5. How does factorization help classify numbers into these categories?

Tip:

To determine if a number is prime, test its divisibility by all prime numbers less than or equal to its square root.