Prime number is one that cannot be decomposed into factors except 1 and itself (numbers 2 3 5 7 are prime.) see factoring

Explanation:

All natural numbers have at least two factors: one and the same. see what is a divisor

There are numbers that also have other factors

Examples:

• 15 = 1·15 = 3·5 (factors of 15: 1,3,5,15)
• 12 = 1·12 = 2·6 = 3·4 (factors of 12: 1,2,3,4,6,12)
• 7 = 1·7 (factors of 7: 1,7)

In this example, the number 7 is prime because it only can be factorized by 1 and itself  A number is prime if there aren’t more factors than itself and unity.

Conclusions

Prime number is one that can not be obtained by the multiplication of 2 numbers. (Except the same by 1) see what is a multiple

Prime number is the number that can not be obtained by multiples of any number (except 1 and itself) In this table we can see:

In red the multiples of 2 except 2

In blue multiples of 3 except 3

In green multiples of 5 except 5

and so on, with 7 (red triangle), 11 (blue triangle), 13 (green triangle)

The numbers have remained unchecked are the prime numbers up to 30, finds that none can be decomposed into prime factors. see factoring