Prime Numbers

A prime number is defined as an integer that is greater than 1, and has only two positive factors, 1 and itself.

For example, 7 is a prime number, as its only factors are 1 and 7.

However, 6 is not a prime number, because its factors are 1, 2, 3, 6

The first ten prime numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29

Note, though that 1 is not a prime number, and both the smallest and the only even prime number is 2.

Prime factorization is the process by which you express a number as a result of only prime numbers.

For example:

To create the prime factorization of 24, you’d represent it as:

2 x 2 x 2 x 3 or 23 × 3

To create the prime factorization of 15, you’d represent it as:

5 x 3

24

An example of a factor question is:

If xy = 13 and both x and y are positive integers, then what is the sum of x + y?

A. 13

B. 14

C. 16

D. 20

E. 26

Note: the answer is B

Here is another example:

What is the sum of the first 5 prime numbers?

A. 18

B. 28

C. 30

D. 34

E. 38

Note: The first five prime numbers are 2, 3, 5, 7, 11 and their sum is 28. The answer is B.