Why does WolframAlpha say that this series $$\sum_{n=1}^{\infty} \frac{1}{n^{\frac{a}{2}-2}}$$ converges only if $a>6$? Shouldn't it be $a\ge 6$?


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    $\begingroup$ When $a=6$ you get the harmonic series, which diverges. There are many proofs of this. $\endgroup$ – Hendrix Nov 14 '19 at 17:09
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    $\begingroup$ The last I heard, $\sum\frac1n$ was still divergent. $\endgroup$ – Angina Seng Nov 14 '19 at 17:10

It must be $$\frac{a}{2}-2>1$$ so $$a>6$$

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