Example 1 from this review of power series and the ratio test is:
$\sum\limits_{n = 0}^\infty {\frac{{{{\left( { - 3} \right)}^n}}}{{n\,{7^{n + 1}}}}{{\left( {x - 5} \right)}^n}}$
It converges by the ratio test. But isn't the first term of this series undefined since it contains $n = 0$ in the denominator?
That is,
$a_0 = {\frac{{{{\left( { - 3} \right)}^0}}}{{0\,{7^{1}}}}{{\left( {x - 5} \right)}^0}} = \frac{1}{0}$
Thank you.