And what is a prime? Only that way will you be able to ... ARCHIMEDES:Yes, seven is a factor of 21 because you can multiply it by another number to give 21. We get seven each.

The highest common factor (abbreviated to HCF) is the largest number that goes into two or more subject-numbers. For example, the common factors of 40 and 16 are 2, 4 and 8. The HCF of 40 and 16 ...