1-(7^1/10)^50

$${\mathtt{1}}{\mathtt{\,-\,}}{\left({\frac{{{\mathtt{7}}}^{{\mathtt{1}}}}{{\mathtt{10}}}}\right)}^{{\mathtt{50}}} = {\mathtt{0.999\: \!999\: \!982\: \!015\: \!349\: \!6}}$$

Or did you mean this???

$${\mathtt{1}}{\mathtt{\,-\,}}{\left({{\mathtt{7}}}^{\left({\frac{{\mathtt{1}}}{{\mathtt{10}}}}\right)}\right)}^{{\mathtt{50}}} = -{\mathtt{16\,806.000\: \!000\: \!000\: \!000\: \!000\: \!9}}$$

.