Oh, wow, that's a huge number for a short time, and it's actually a best seller number. So i guess the book should be: 1.- Really good. 2.- Written by a best-seller author who's already known 3.- Have an incredible marketing strategy behind with a few dollars on the budget.
I couldn't help you with the first 2 items, but i could with the third if 1 or 2 applies. Hope that helps! Have a nice day, and i wish you success!