Addition : Addition is the mathematical operation that describes increasing a number by an amount equal to a second number. The mathematical symbol for addition is the plus sign $+.$ The term addition is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.

Digit : A digit is a symbol used in the representation of a number.

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 4 : An integer $x$ is called divisible by 4 if $x$ is a multiple of 4. An integer is divisible by 4 if and only if the last two digits form a number that is divisible by 4.

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

Addition : Addition is the mathematical operation that describes increasing a number by an amount equal to a second number. The mathematical symbol for addition is the plus sign $+.$ The term addition is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.

Counterexample : A counterexample to a statement of the form 'all objects of type x have property y' is an object of type x that does not have property y. A counterexample to a statement shows that the statement is not true in general. For example the number 3 is a counterexample to the statement that all numbers are even.

Integer : An integer is any ot the numbers $\ldots, -3, -2, -1, 0, 1, 2, 3, \ldots.$

Multiplication : Multiplication is the mathematical operation that is a shorthand for adding the same amount several times. For example $3\cdot 4=4+4+4=12.$

Non-zero : Not equal to the number 0.

Subtraction : Subtraction is the mathematical operation that describes decreasing a number by an amount equal to a second number. The mathematical symbol for subtraction is the minus sign $-.$ The term subtraction is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.