Let 0<a<1. I'm trying to figure out whether the following series converges:
∞∑k=1ka1k(k+1).
Now it's clear that if a were greater than or equal to 1 then this series would diverge since
∞∑k=1k11k(k+1)=∞∑k=11(k+1)=∞∑k=21k=∞.
So this makes it a bit hard to think of a bound for the series in question. Any advice?
Answer
0≤kαk(k+1)≤1k2−α,
and 2−α>1.
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