Mathematics

Mathematics

Problem

Suppose det⁡[∑k=0nk∑k=0nnCkk2∑k=0nnCkk∑k=0nnCk3k]=0\det \begin{bmatrix} \sum_{k=0}^{n} k & \sum_{k=0}^{n} {}^{n}C_{k} k^{2} \\ \sum_{k=0}^{n} {}^{n}C_{k} k & \sum_{k=0}^{n} {}^{n}C_{k} 3^{k} \end{bmatrix} = 0 holds for some positive integer nn. Then ∑k=0nnCkk+1\sum_{k=0}^{n} \frac{{}^{n}C_{k}}{k+1} equals __.

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