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$$
{\operatorname  {erfc}}(x)={\frac  {2}{{\sqrt  {\pi }}}}\int _{x}^{{\infty }}e^{{-t^{2}}}\,dt={\frac  {e^{{-x^{2}}}}{x{\sqrt  {\pi }}}}\sum _{{n=0}}^{\infty }(-1)^{n}{\frac  {(2n)!}{n!(2x)^{{2n}}}}
$$
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