Does the series ∞∑2lognn(loglogn)2
converge?
The root and ratio tests are inconclusive, the integral test may be too difficult to apply. I've tried the limit comparison test with logn/n but that is also inconclusive since lognn(loglogn)2lognn=1(loglogn)2→0.
Answer
Using the Cauchy condensation test, (cf Wikipedia), your series diverges.
The transformed series reads :
∑n2nn2nlog2n=∑nnlog2n
Remark : I interpreted log as a base two logarithm, which does not affect the result
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