Count : To count means to find out the number of objects by adding one for every object.

Divisible : An integer $x$ is called divisible by an integer $y$ if the division $x:y$ has a remainder of zero. For example 4 is divisible by 2 but 5 is not divisible by 2.

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 6 : An integer $x$ is called divisible by 6 if $x$ is a multiple of 6. An integer is divisible by 6 if and only if it is even and the sum of its digits is divisible by 3.

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

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.

Greatest common factor : The greatest common factor of two natural numbers $m$ and $n$ is a natural number $k$ that is a factor of $m$ and $n$ such that there is no bigger number that is also a factor of $m$ and $n.$ For example the greatest common factor of 12 and 15 is 3. To simplify a fraction one can divide both the numerator as well as the denominator by the greatest common factor of the numerator and the denominator. The exponents in the prime factorization of the greatest common factor of two numbers are the minima of the exponents in the prime factorization of the two numbers.

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