When flipping a coin 17 times in a row, there are 2^17 = 131,072 possible outcomes of head/tail sequences. The chances of getting a particular outcome (all heads) is then 1/131,072.
The problem with your math is that 0.00000762939 (7.62939e-6) expressed as a fraction is not 19/25,000,000. It's 1/131,072.