Number

Types of number

Natural numbers: $1, 2, 3, \dots$ (counting numbers).
Integers: $\dots, -2, -1, 0, 1, 2, \dots$ (whole numbers, positive and negative).
Rational numbers: any number that can be written as a fraction $\frac{a}{b}$ where $a, b$ are integers and $b \neq 0$ (includes terminating and recurring decimals).
Irrational numbers: cannot be written as a fraction, e.g. $\pi$ and $\sqrt{2}$ (non-terminating, non-recurring decimals).
Prime numbers: exactly two factors, 1 and itself ($2, 3, 5, 7, 11, \dots$). Note: 1 is not prime.