How to evaluate series $$\sum_{n=0}^\infty\frac{5n+1}{(2n+1)!}$$ I tried to split the summation...but I failed. Please help
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Is this the sum you're trying to evaluate? – user170231 May 21 '19 at 16:34
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Yes. Summation n running from 0 to infinity – user538954 May 21 '19 at 16:35
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https://math.stackexchange.com/questions/576976/evaluate-the-series-lim-limits-n-to-infty-sum-limits-i-1n-fracn22/576978#576978 – lab bhattacharjee May 21 '19 at 18:03
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Hint: $$5n+1 = \frac{5}{2}(2n+1) - \frac{3}{2}$$
Do you know $\sum_{n=0}^\infty \frac{1}{(2n+1)!}$ and $\sum_{n=0}^\infty \frac{1}{(2n)!}$ ?
Robert Israel
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Thank you. We can group the terms accordingly to get the answer $\frac{e}{2}+\frac{2}{e}$ – user538954 May 21 '19 at 16:44
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$$\sinh x=\sum_{n=0}^{\infty}\frac{x^{2n+1}}{(2n+1)!}$$ $$\frac{1}{x}\sinh x=\sum_{n=0}^{\infty}\frac{x^{2n}}{(2n+1)!}$$ let $x\rightarrow \sqrt{x}$ $$\frac{1}{\sqrt{x}}\sinh \sqrt{x}=\sum_{n=0}^{\infty}\frac{x^{n}}{(2n+1)!}$$
let $x\rightarrow x^5$ $$\frac{1}{\sqrt{x^5}}\sinh \sqrt{x^5}=\sum_{n=0}^{\infty}\frac{x^{5n}}{(2n+1)!}$$ multiply by $x$ $$\frac{x}{\sqrt{x^5}}\sinh \sqrt{x^5}=\sum_{n=0}^{\infty}\frac{x^{5n+1}}{(2n+1)!}$$ $$(\frac{x}{\sqrt{x^5}}\sinh \sqrt{x^5})'=\sum_{n=0}^{\infty}\frac{(5n+1)x^{5n}}{(2n+1)!}$$ then let $x=1$ to get the sum
E.H.E
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