Divisible by 2 : An integer $x$ is called divisible by 2 if $x$ is a multiple of 2. An integer is divisible by 2 if and only if it is even.

Divisible by 3 : An integer $x$ is called divisible by 3 if $x$ is a multiple of 3. An integer is divisible by 3 if and only if the sum of its digits is divisible by 3.

Factor : If a natural number is divisible by a second natural number, that second natural number is called a factor of the first natural number. For example the factors of 12 are 1,2,3,4,6 and 12.

Number : A number $x$ is a mathematical symbol representing a quantity.

Prime number : A prime number is a natural number bigger than 1 that only has 1 and itself as a factor. The first five prime numbers are 2, 3, 5, 7 and 11. There is an infinite number of prime numbers.