Is there a closed form for this product? $$\prod\limits_{k=1}^n (n+k)$$ I checked it on wolfram alpha but it uses something called the Pochhammer symbol. Does anyone else know of a nice explicit closed form or some type of trick to calculate this thing without using the Pochhammer symbol? Any help is appreciated. Thanks.
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4$(2n)!/n!{}{}{}$ – Gerry Myerson Mar 12 '14 at 06:27
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$$\prod_{k=1}^n(n+k)=\prod_{k=n+1}^{2n}k=\frac{\displaystyle\prod_{k=1}^{2n}k}{\displaystyle\prod_{k=1}^nk}=\color{blue}{\frac{(2n)!}{n!}}=n!\cdot\frac{(2n)!}{n!^2}=\color{blue}{n!\cdot{2n\choose n}}$$
Lucian
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+1 thank you! So simple. I was really tired when I posted this. It makes perfect sense now :) – homegrown Mar 12 '14 at 16:03