As n ranges over the positive integers, what is the sum of all possible values of the greatest common divisor of 3n+4 and n?

If we start listing out the gcds, you'll notice that they repeat, 1, 2, 1, 4. 

I'm pretty sure this is due to the +4 in 3n + 4. 

So the possible values are 1, 2, and 4. 

1 + 2 + 4 = 7

I hope this helped. :)))

 

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