Need help proving convergence of this series

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    Convergence Series
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Discussion Overview

The discussion revolves around the convergence of the series defined by the terms n! / n^n. Participants explore both numerical and analytical approaches to establish convergence, considering various mathematical tests and properties of sequences.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant claims to have proven numerical convergence but struggles with an analytical proof, suggesting the series may not converge.
  • Another participant suggests finding a relation between the n-th term and the n+1-th term or using Stirling's approximation for asymptotic behavior.
  • A third participant recommends using the ratio test to analyze convergence.
  • One participant notes that the sequence is decreasing and bounded by 0, invoking the monotone convergence theorem to assert it converges to some number. They argue that for the series to converge, the sequence must approach 0, which they claim it does, and propose using the squeeze theorem.
  • This participant further states that by the p-test, the series with terms x_n = 1/n^2 converges, and thus, by the comparison test, the series with terms x_n = n!/n^n also converges.

Areas of Agreement / Disagreement

Participants present multiple approaches and tests for establishing convergence, but there is no consensus on the analytical proof or the overall convergence of the series. Some methods are suggested, but the discussion remains unresolved regarding the definitive convergence of the series.

Contextual Notes

Limitations include the dependence on the assumptions made about the sequence and series, as well as the potential need for further clarification on the application of the comparison test and the squeeze theorem.

swampwiz
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n! / nn

I have proven that the sequence converges numerically, but I can't do it analytically, and can't do anything for the series (maybe it the series doesn't converge?)
 
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Can you find a relation between the n-th term and the n+1-th term?

Or if you want the asymptotic behavior you can use the stirling's approximation
 
Use the ratio test
 
First note its a decreasing sequence bounded by 0, so by the monotone convergence thereom it converges to some number.

If the series is going to converge, the sequence needs to go to 0, which it does as n!/n^n <= 1/n^2 (so use the squeze theorem).

By the p test(you could also use ratio test), we know the series where x_n = 1/n^2 converges.

Thus by the comparision test we see that the series with x_n = n!/n^n converges.
 

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