Factors can be thought of as the multiplying building blocks for integers. A factor is an integer that divides another integer without leaving a remainder. In general, an integer x is a factor of the integer y if is also an integer.

Because 8 divides 24 evenly (as 3), with no remainder, 8 is a factor of 24. Eight factors into 2 × 2 × 2. Hence, the integer 24 is made up of the factors 2, 2, 2, and 3 multiplied together.

Every integer is a factor of itself, because it divides itself evenly, with no remainder. Also, 1 is a factor of every number. All integers therefore have factors, because each integer (except 0) has at least two factors—1 and itself.

When an integer has only two factors, then it is a prime number. Because the only factors of 5 are 1 and 5, 5 is a prime number. When a number has more than two factors, then it is a composite number. Besides 1 and 15, 15 has two...