Number Theory

First, let's subtract the to numbers and see what we get. 

We get $123 - 47 = 76$

Now, we need to find the prime factors of 76. 

When we factorize it, we get $76 = 2^2 \cdot 19$

This means there are only two distinct prime factors. $2, 19$

Adding these two up, we get $19+2=21$

So 21 is our final answer!

Thanks! :)