Question: what is the least common multiple of 9 and 21 using prime factorization?
Answer: Alternatively, the lcm of 9 and 21 can be found using the prime factorization of 9 and 21: The prime factorization of 9 is: 3 x 3. The prime factorization of 21 is: 3 x 7. Eliminate the duplicate factors of the two lists, then multiply them once with the remaining factors of the lists to get lcm(9,9) = 63.