Can Ʃ (anbn) be divergent if Ʃan and Ʃbn are both convergent?

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SUMMARY

The discussion centers on the mathematical inquiry of whether the series Ʃ(anbn) can diverge when both Ʃan and Ʃbn are convergent. Participants emphasize the importance of absolute convergence, noting that if both series are absolutely convergent, then Ʃ(anbn) must also converge. However, the challenge lies in identifying specific examples where Ʃ(anbn) diverges despite the convergence of Ʃan and Ʃbn. The consensus suggests exploring series that are convergent but not absolutely convergent to find suitable examples.

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Ryuzaki
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Homework Statement



Show by example that if Ʃan and Ʃbn are two convergent series, then Ʃ (anbn) may be a divergent series.

Homework Equations



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The Attempt at a Solution



I've been trying long and hard to find an example for this particular case, but I'm unable to find one. I've found examples where Ʃan and Ʃbn are divergent, but Ʃ(anbn) is convergent. Can anyone please give an example? Thanks.
 
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I think it's true that if Ʃan and Ʃbn are absolutely convergent, then also Ʃanbn converges. So maybe consider series which are convergent, but not absolutely convergent.
 

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