A factor string is a whole number written as a multiplication problem with two or more factors other than one, according to the Southampton Public Schools. For example, 3 x 3 x 3 is a factor string for the 27.
A factor is one of the numbers that is multiplied to find a product in a multiplication problem. Factor strings break whole numbers down into their factors. Some factor strings contain composite numbers. For example, 24 x 3 is a factor string for 72. Prime factor strings only contain prime numbers. For example, 7 x 13 x 2 is a prime factor string for 182. Each composite whole number has only one corresponding prime factor string.