Numbers that have no common factors other than 1. Also called "relatively prime" or "mutually prime."

21 and 22 are coprime:

• The factors of 21 are 1, 3, 7 and 21

• The factors of 22 are 1, 2, 11 and 22

(the only common factor is 1)

But 21 and 24 are NOT coprime:

• The factors of 21 are 1, 3, 7 and 21

• The factors of 24 are 1, 2, 3, 4, 6, 8, 12 and 24

(the common factors are 1 AND 3) Numbers you can multiply to get another number. In other words: Numbers that go into other numbers evenly.

Ex: 1, 3, 5, & 15 are all factors of 15 because they can be divided into 15 evenly

In the same manner, 15 is a "multiple" number for 1, 3, 5, &15.

Another Ex: 1, 2, 3, 4, 6, 12 are all factors of their multiple: 12

NOTE: -1, -2, -3, -4, -6, -12 are all the negative factors of 12.