What is the gcf of 15 and 64?

The greatest common factor (GCF) of 15 and 64 is 1. This is because the only common factor that these two numbers share is 1. The GCF is the largest number that divides both numbers without leaving a remainder. In this case, since 1 is the only number that can do that for both 15 and 64, the GCF is 1.