What is the greatest common factor of 21 49 and 63?

To find the greatest common factor (GCF) of 21, 49, and 63, we first need to find the prime factorization of each number. The prime factorization of 21 is 3 x 7, 49 is 7 x 7, and 63 is 3 x 3 x 7. The GCF is the product of the common prime factors raised to the lowest power they appear in all the numbers, which in this case is 7. Therefore, the GCF of 21, 49, and 63 is 7.