 ## How to find the Least Common Multiple of 15 and 21?

On this page below, we'll use the Prime Factorisation, and the List of Multiples method to find out the LCM of 15 and 21.

Follow the steps below, and let's calculate the LCM of 15 and 21.

### Method 1 - Prime factorization

#### Step 1: Create a list of all the prime factors of the numbers 15 and 21:

##### Prime factors of 15

The prime factors of 15 are 3 and 5. Prime factorization of 15 in exponential form is:

15 = 31x51

##### Prime factors of 21

The prime factors of 21 are 3 and 7. Prime factorization of 21 in exponential form is:

21 = 31x71

31, 51, 71

31x51x71=105

#### Step 4: The result:

As seen on the calculation above, we have now obtained the LCM of 15 and 21.

The Least Common Multiple of 15 and 21 is 105.

### Method 2 - List of Multiples

Find and list multiples of each number until the first common multiple is found. This is the lowest common multiple.

#### Multiples of 15:

15, 30, 45, 60, 75, 90, 105, 120, 135, 150

#### Multiples of 21:

21, 42, 63, 84, 105, 126, 147, 168

#### Therefore,

LCM(15, 21) = 105