Types of Number

Real Numbers

ℕ = {1, 2, 3, 4, 5, ...}

ℤ = {... -2, -1, 0, 1, 2, ...}

Even Numbers = {... -4, -2, 0, 2, 4, ...} = {2 n : n \in ℤ}

Odd Numbers = {... -3, -1, 1, 3, 5, ...} = {2 n - 1 : n \in ℤ}

A number with only two factors: one and itself

Examples:

5 = 1 \times 5

31 = 1 \times 31

11939 = 1 \times 11939

A number that can be written as a product of two or more prime numbers.

Examples:

6 = 2 \times 3

72 = 2^{3} \times 3^{2}

2310 = 2 \times 3 \times 5 \times 7 \times 11

ℚ = {p / q : p \in ℤ, q \in ℕ}