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If Dk=1nn2k n^2+n+1n^2+n2k-1n^2n^2+n+1a ...

If `D_k=1nn2k n^2+n+1n^2+n2k-1n^2n^2+n+1a n dsum_(k=1)^n D_k=56.` then `n` equals `4` b. `6` c. `8` d. none of these

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