Pre Algebra Question - Finding the LCM of 57 and 63

Hi

I am not taking classes or anything, but I want to learn more math and I am basically starting near the bottom. Right now I am working on finding the LCM of a set of numbers and was finding it pretty easy until these two number (57, 63) started giving me problems.

I am working out of a book and the instructions it gives for finding the LCM are to find the prime factors of each number, underline the most repeated occurence of a number in the factorization and finally to multiply all the numbers together.

So for 57 I found that the prime factors are: 3 & 19

And for 63 the prime factors are: 7, 3 & 3

With the number 57, the numbers 3 and 19 each occur one time. And with 63 the most common occurence is the number 3. So here is what I tried to do...

3 x 3 x 3 x 19 = LCM 513 (obviously this isnt correct)

So I checked online and used a LCM calculator and found out that the LCM is actually 1197. The only way I can come up with this number is to multiply 3 x 3 x 7 x 19.

Can someone help me understand what I am doing wrong? I am afraid it is some simple oversight on my part.

Thanks