What is the greatest common factor for 21 and 40?

To get the Greates Common Factor (GCF) of 21 and 40 we need to factor each value first and then we choose all the copies of factors and multiply them:

21: 3 7 40: 222 5 GCF: The Greates Common Factor (GCF) is: 1

The only common factor is 1. So that's the greatest.