The number 27 is not a prime number because it is evenly divisibleÂ by 1, 3, 9 and 27. A prime number is a number only divisible by 1 and the number itself. Since 27 is divisible by other numbers, it is considered a composite number.
The way to determine whether a number is prime or composite is to determine its factors. Factors are numbers that are evenly divisible into a number. If the number can be evenly divided by numbers other than 1 and itself, then it is not prime.
To find the factors for the number 27, a person would determine which numbers from 1 to 27 divide evenly into the number. For example, 27 can be divided by 1 to get 27, and 27 can be divided by 9 evenly three times. Therefore, the factors of 27 are 1, 3, 9 and 27, so it cannot be prime.