1. Natural Numbers

Numbers from 1 and go on: 1, 2, 3, 4, 5, …

2. Whole Numbers

Natural numbers plus 0: 0, 1, 2, 3, …

3. Integers

Positive, negative numbers and 0: … -3, -2, -1, 0, 1, 2, …

4. Even Numbers

End with 0, 2, 4, 6, 8: 2, 4, 6, 8, 10, …

5. Odd Numbers

End with 1, 3, 5, 7, 9: 1, 3, 5, 7, 9, …

6. Prime Numbers

Only 2 factors: 2, 3, 5, 7, 11, …

7. Composite Numbers

More than 2 factors: 4, 6, 8, 9, …

8. Rational Numbers

Can be written as fractions: 1/2, 3/4, 5/1

9. Irrational Numbers

Cannot be written as fractions: √2, π

10. Decimal Numbers

Contain a dot: 3.5, 2.75, …

11. Roman Numbers

Old-style: I, V, X, L, C

Fun Facts: 0 is neither positive nor negative. 2 is the only even prime. Numbers go on forever (∞).