Question: what is the greatest common factor between 12 and 13?
Answer: The prime factorization of 12 is: 2 x 2 x 3.
The prime factorization of 13 is: 13.
The prime factors and multiplicities 12 and 13 have in common are: 1.
1 is the gcf of 12 and 13.
gcf(12,13) = 1.