# Looks like a reciprocal binomial

Algebra Level 4

Suppose we denote $$\displaystyle a_n$$ as the value of $$\displaystyle \sum_{r=0}^n \dfrac1{^n C_r }$$, express $$\displaystyle \sum_{r=0}^n \dfrac r{^n C_r}$$ in terms of $$n$$ and/or $$a_n$$.

Clarification:

$$^n C_r$$ denote the binomial coefficient, $$\dbinom{n}{r} = \dfrac{n!}{r!(n-r)!}$$.

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