I'm trying to find out whether this Series
∑∞n=2an converges or not when
an=1log(n!)
I tried couple of methods, among them: d'Alembert an+1an, Cauchy condensation test ∑∞n=22na2n, and they both didn't work for me.
Edit: I can't use stirling, and integral.
Thank you
Answer
Hint: You can use an=1logn!=1∑nk=1logk≥1nlogn.
Then use the Cauchy condensation test...
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