binomial theorem

if a(n)=sigma lower notation(r=0) and upper notation(n) expression to be summated (1/(nCr) then same sigma but expression to be summated (r/(nCr) equals ?? http://www.texify.com/img/%5CLARGE%5...D%20a%20_n.gif for first

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Originally Posted by prasum

if a(n)=sigma lower notation(r=0) and upper notation(n) expression to be summated (1/(nCr) then same sigma but expression to be summated (r/(nCr) equals

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I hope this helps.

$\displaystyle a_n = \sum\limits_{r = 0}^n {\dbinom{n}{r}^{-1}}=\sum\limits_{r = 0}^n {\dfrac{r!(n-r)!}{n!}} $