Tuesday, April 10, 2018

real analysis - Does the series sumlimitsinftyn=1left(1fracln(n)nright)2n diverge?



could anyone help me figure out whether this infinite series
n=1(1ln(n)n)2n


diverges?



I've tried using Cauchy's and d'Alembert's limit tests but both gave the result 1. I've also tried the necessary condition for convergence, but
limn(1ln(n)n)2n=0


Answer




Use



n=1(1lognn)2nn=1(exp(lognn))2n=n=1exp(2logn)=n=11n2<.


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