# SAT Study Guide/Part 2 - The Math Section/General Numerical Concepts

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## Number properties[edit]

There are several sets of numbers:

- Counting or Natural numbers are numbers that can be used to count real things:
- Integers (including 0) include the natural numbers and their opposites:
- Even integers are divisible by 2; you can express even integer as , where is any integer:
- Odd integers are not divisible by 2; you can express any odd integer as , where is any integer:

- Rational numbers are numbers you can express as a fraction , where and cannot simplify the other:
- Irrational numbers are non-repeating, non-terminating decimals that you cannot express as a ratio or division of intergers , where and cannot simplify the other:
- Real numbers include all of the above.

Numbers can be *prime*. That is, they are divisible by themselves and one, only. 1 is not considered a prime number, and 2 is the only even prime number. The first eight prime numbers are: