The factors of 18 are one, two, three, six, nine and 18. Each number has factors that when multiplied together, add up to equal that number. The number 18 has a total of 6 factors from three different equations: 1x18, 2x9 and 3x6. When trying to find the factor for a particular number, the focus is on searching for whole numbers that are equal to it or of lesser value.
The key to finding all the factors of a number is to know all common multiples available. Every number has at least two factors because one and the number itself can be multiplied to give that number. Occasionally, numbers have only one and that number as factors, and these numbers are called "prime numbers". For example, 17 is a prime number because the only factors for it are one and 17. No other whole number can be used in a multiplication equation to get 17.
When dealing with the factors of two different numbers, the greatest common factor can be found by looking for the highest factor that each number has in common. For example, for 18 and 27, the greatest common factor is 9, as this number can be multiplied, by two and three respectively, to get each answer. The number three is also a factor for both 18 and 27, but it is not the great common factor available.