\[\boxed{\mathbf{669}.}\]
\[1)\ y = 5^{\frac{1}{x}};\ \ \ x \neq 0\]
\[D(x):\ \ \ x \neq 0.\]
\[2)\ y = 7^{\sqrt{x - 1}}\]
\[x - 1 \geq 0\]
\[x \geq 1.\]
\[D(x):\ \ x \geq 1.\]
\[3)\ y = {0,4}^{\frac{1}{x - 9}}\]
\[x - 9 \neq 0\]
\[x \neq 9.\]
\[D(x):\ \ x \neq 9.\]
\[4)\ y = {0,8}^{\frac{1}{|x| - 2}}\]
\[|x| - 2 \neq 0\]
\[|x| \neq 0\]
\[x \neq \pm 2.\]
\[D(x):\ \ x \neq \pm 2.\]