Numbers:

• Natural/counting numbers or positive integers are 1, 2, 3, …
• Whole numbers are 0, 1, 2, 3, 4, …
• The numbers -2, -1, 0, 1, 2, … are called integers.
• The numbers -3, -2, -1, are described as negative integers.
• Fractions in the form 5/2 or 9/10 are called rational numbers. Numbers such as 5 can be expressed as 5/1, therefore all integers are rational numbers. All rational numbers can be expressed as a/b, with a being an integer and b being a positive integer. Terminating and repeating decimals are also regarded as rational numbers, as they can be written as fractions in the form just mentioned.
• Irrational numbers cannot be expressed as fractions in the form a/b with being an integer and being a natural number. $\sqrt { 2 }$ and $\pi$ are examples of irrational numbers. Irrational numbers when expressed as a decimal don’t terminate and don’t have a repeating decimal pattern.
• Even numbers (2n) are divisible by two, for example: -8, -6, -4, -2, 0, 2, 4, 6, 8.
• Prime numbers are natural numbers that have two different factors, or more specifically, they can only be divided by one and themselves. Numbers such as 2, 3, 5, 7, 11, 13, 17, 19, 23 and 29 are prime numbers.
• Odd numbers (2n+1) are integers that aren’t divisible by two. Integers such as -5, -3, -1, 1, 3, 5, 7, …
• Squares are results obtained when numbers get multiplied by themselves. 4×4=16, 5×5=25 6×6=36, therefore 16, 25 and 36 are squares.

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