If it's not what You are looking for type in the calculator fields your own values, and You will get the solution.
To get the Greates Common Factor (GCF) of 426 and 639 we need to factor each value first and then we choose all the copies of factors and multiply them:
|426: ||2||3|| ||71|
|639: || ||3||3||71|
|GCF: || ||3|| ||71|
The Greates Common Factor (GCF) is: 3 x 71 = 213