Saturday, August 4, 2018

real analysis - Limit of left(1frac122right)left(1frac133right)dotsleft(1frac1nnright) as ntoinfty



So I'm trying to solve the following limit:



lim



Now, I tried getting the squeeze theorem around this one, since it does feel like something for the squeeze theorem. The upper bound is obviously 1, but since each term decreases the product, it may seem like this approaches zero?


Answer



\begin{align} \prod_{n=2}^\infty\left(1-\frac1{n^n}\right) &\ge\prod_{n=2}^\infty\left(1-\frac1{n^2}\right)\\ &=\lim_{m\to\infty}\prod_{n=2}^m\frac{n-1}n\frac{n+1}n\\ &=\lim_{m\to\infty}\prod_{n=2}^m\frac{n-1}n\prod_{n=2}^m\frac{n+1}n\\ &=\lim_{m\to\infty}\frac1m\frac{m+1}2\\[6pt] &=\frac12 \end{align}
So the product converges (that is, it is bounded away from 0). However, numerically, the product is approximately 0.71915450096501024665446931 and the Inverse Symbolic Calculator does not find anything for this number.



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