Question: what is the greatest common factor between 69 and 21?
Answer: The prime factorization of 21 is: 3 x 7. The prime factorization of 69 is: 3 x 23. The prime factors and multiplicities 21 and 69 have in common are: 3. 3 is the gcf of 21 and 69. gcf(21,69) = 3.