### Numbers: Integers

### Prime numbers

We have seen that we cannot factorize the number #7#. Numbers with this property are part of a special group of numbers with an important role in mathematics.

Prime number

The integer #5# has exactly two divisors, namely #1# and #5#.

The integer #13# has exactly two divisors, namely #1# and #13.#

The numbers #5# and #13# are examples of **prime numbers.**

*A prime number is a positive integer which has exactly two divisors: #1# and itself.*

The list of prime numbers begins as follows: \[\begin{array}{c}

2,3,5,7,11,13,17,19,23, 29,31, \\

37,41,43, 47, 53, 59, 61, 67, 71, 73, \\

79, 83, 89, 97, 101, 103, 107, 109,113, \\

127, 131, 137, 139, 149, 151, 157 \ldots \end{array}\]

No

No, #18# has more than #2# divisors, namely #1,2,3,6,9,18#.

No, #18# has more than #2# divisors, namely #1,2,3,6,9,18#.

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