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Grandi's Series


Grandi's series is the divergent series

 1-1+1-1+....

Its partial sums alternate between 1 and 0, so the series does not converge in the ordinary sense. The arithmetic means of the partial sums converge to 1/2, and the associated power series satisfies

 1-x+x^2-x^3+...=1/(1+x) for |x|<1,

whose limit as x->1^- is also 1/2. Thus Grandi's series is both Cesàro summable and Abel summable to 1/2.


See also

Abel-Regularized Sum, Arithmetic Mean, Cesàro Sum, Convergence, Divergent Series

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References

Hardy, G. H. Divergent Series. Providence, RI: Amer. Math. Soc., 1991.

Cite this as:

Weisstein, Eric W. "Grandi's Series." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/GrandisSeries.html

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