A factor divides a number exactly; a multiple is what you get by multiplying.
The HCF (highest common factor) is the largest factor two numbers share: HCF of 12 and 18 is 6. The LCM (lowest common multiple) is the smallest multiple they share: LCM of 4 and 6 is 12.
A prime number has exactly two factors — 1 and itself: 2, 3, 5, 7, 11, …
Remember
- HCF = biggest shared factor · LCM = smallest shared multiple.
- A prime number has exactly two factors.