$T_ r$ is a sequence such that

$\sum_{r =1 } ^ n T_r = \frac{ n(n+1)(n+2)(n+3) } { 8 }.$

$\displaystyle \sum_{r=1}^{11} \frac{1}{T_r } = \frac{a}{b}$, where $a, b$ are coprime positive integers. Find $a + b$.

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