Hi pcds,
Shall I go ahead and assume you meant your starting viral load was 1, 700,000 and not "1,7000,000"?
At any rate, the fast and oh-so-easy way to calculate a viral load log drop is to knock off the last zeros from the end of the number, for example:
1,700,000 (assuming that's the number you meant)
170,000 = one log drop
17,000 = two log drop
1700 = three log drop
You can also use an online calculator's ‘LOG’ function. Input viral load, press LOG and voila.