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Clearly, it is an A.P. with first term $1$ and common difference $1$.

Let $S_{n}$ denote the required. Then,

$S_{n}=2n (1+n)$ $[Using:S_{n}=2n (a+l)]$

$⟹S_{n}=2n(n+1) $

$S_{n}=2n (1+n)$ $[Using:S_{n}=2n (a+l)]$

$⟹S_{n}=2n(n+1) $

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