Infinite(simal) Sum

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Find a formula for \(\sum_{i=0}^\infty i^{2014}x^{i}\). In other words, find \(0^{2014}x^{0}+1^{2014}x^{1}+2^{2014}x^{2}+3^{2014}x^{3}+4^{2014}x^{4}+...\).

Hint: Try a form of recursion(not with numbers, but with a formula).

Note by Tristan Shin
7 years, 2 months ago

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Comments

We can get a recurrence relation in the following manner:

For positive integers k we define Tk(x)=i=0ikxiT_{k}(x)=\sum_{i=0}^{\infty }i^kx^i x(0,1)\forall x \in (0,1)

We know T1(x)=x(1x)2T_{1}(x)=\frac{x}{(1-x)^2}

Also Tk+1(x)=xdTk(x)dxT_{k+1}(x)=x\frac{dT_{k}(x)}{dx}

Sambit Senapati - 7 years, 2 months ago

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To be precise, is there a way of expanding your recursion formula?

Tristan Shin - 7 years, 2 months ago

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Sorry, I didnt get you. What do you exactly mean by expanding the recursion formula? Did you mean this-

Tk+1(x)=Tk(x)+x2Tk1(x)T_{k+1}(x)=T_{k}(x)+x^2T_{k-1}''(x)

Sambit Senapati - 7 years, 2 months ago

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@Sambit Senapati I found a simpler recursion formula that only reaches back one term.

For a start, I labeled Tk=f(x)(1x)k+1T_{k}=\frac {f(x)}{(1-x)^{k+1}}. Then, try working around with that.

Tristan Shin - 7 years, 2 months ago

Just a note, I know how to do it, but it would take a very long time(probably over a month straight) of working out some functions. I'm not really looking for an exact solution(don't actually take the time to do it), but if anyone can discover the method I'm using, that would be wonderful.

Tristan Shin - 7 years, 2 months ago
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