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Inconsistency in summations using Wolfram|Alpha?

Posted 5 years ago

I have recently queried WolframAlpha this way...

sum((1/(5*n+3)+1/(5*n+2))^2*(1/(5*n+4)+1/(5*n+1))^2*(3*n+1),-infinity<=n<=infinity)

...getting about -0.585507.

But the result is very different with queries like these ones...

sum((1/(5*n+3)+1/(5*n+2))^2*(1/(5*n+4)+1/(5*n+1))^2*(3*n+1),-1E20<=n<=1E20)
sum((1/(5*n+3)+1/(5*n+2))^2*(1/(5*n+4)+1/(5*n+1))^2*(3*n+1),-1E20<=n<1E20)
sum((1/(5*n+3)+1/(5*n+2))^2*(1/(5*n+4)+1/(5*n+1))^2*(3*n+1),-1E30<=n<=1E30)

... all giving about -1.09159.

I am not a mathematician, I can't understand the result -0.585507.

POSTED BY: Alberto Orioli
2 Replies
Posted 5 years ago
POSTED BY: Bill Nelson
Posted 5 years ago

Yes, I have web access to WolframAlpha free version only. Your explanation for the incorrect answer in my case is satisfying.

(The real lesson for me is that also what appears in the first field of the answer-part of WolframAlpha can be affected by computation insufficient time.)

Thank you for the support.

POSTED BY: Alberto Orioli
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