In math, a factor is a number that divides exactly into another number without leaving a remainder.
To get the common factors from a list of numbers we can get all the factors of each number, put them in a list, and pick only the factors that a present in all the lists.
Common factor calculations can be arduous if you are dealing with a lot of numbers. To make life easier you can use this calculator. To use it paste a comma-separated list of numbers in the first text field, hit calculate and you'll get back the common factors plus the greatest common factor.