What is the greatest common divisor of $121^2 + 233^2 + 345^2$ and $120^2 + 232^2 + 346^2$?
I am reasonably sure this is another AoPS question that you should not be asking here.
But I will give you a hint:
there is only one difference with each of the terms.
So it is not that difficult to put the sides in terms of A+k and A
Then it is easy to find the GCD.
You should find it on your own now.
Even without doing this you can find out what a common divisor is just by looking at what the last digit will be with each one.