Generating functions and sums with binomial coefficients

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SUMMARY

The generating function A(x) for the sequence defined by a_n = ∑_{k=0}^n {n+k choose 2k} 2^{n-k} is given by A(x) = (1-2x) / (4x^2 - 5x + 1). The discussion emphasizes the importance of interchanging sums to simplify the derivation of the generating function. Participants noted the complexity of demonstrating that the coefficients derived from A(x) correspond to the sequence a_n, particularly after applying partial fraction decomposition.

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Homework Statement


Show that the generating function A(x) = \sum_n a_n x^n of

a_n = \sum_{k=0}^n {n+k \choose 2k} 2^{n-k}

satisfies

A(x) = \frac{1-2x}{4x^2-5x+1}

Homework Equations


The Attempt at a Solution


A hint was given to "interchange the sums". After doing that, I don't see how to proceed. I also obtained the coefficients by partial fractions on A(x) but it's definitely non-trivial to show these are a_n. Thanks for any help.
 
Last edited:
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Can you show what you got after interchanging the sums?
 
This one is done. Thanks for taking a look!
 

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