Question: what is the greatest common factor gcf of 45 and 81?
Answer: The prime factorization of 81 is: 3 x 3 x 3 x 3. The prime factors and multiplicities 45 and 81 have in common are: 3 x 3. 3 x 3 is the gcf of 45 and 81. gcf(45,81) = 9.