If ${ }^{2 n+1} \mathrm{P}_{n-1}:{ }^{2 n-1} \mathrm{P}_{n}=11: 21$, then $n^{2}+n+15$ is equal to :

Question

If ${ }^{2 n+1} \mathrm{P}_{n-1}:{ }^{2 n-1} \mathrm{P}_{n}=11: 21$,

then $n^{2}+n+15$ is equal to :

Correct Answer

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