Question: what is the greatest common factor between 49 and 21?
Answer: The prime factorization of 21 is: 3 x 7. The prime factorization of 49 is: 7 x 7. The prime factors and multiplicities 21 and 49 have in common are: 7. 7 is the gcf of 21 and 49. gcf(21,49) = 7.