To determine what digit \(6^n\) ends with for any natural number \(n\), we need to examine the pattern of the last digit of successive powers of 6.
Therefore, the correct answer is that \(6^n\) ends with the digit 6.
Consider an A.P. $a_1,a_2,\ldots,a_n$; $a_1>0$. If $a_2-a_1=-\dfrac{3}{4}$, $a_n=\dfrac{1}{4}a_1$, and \[ \sum_{i=1}^{n} a_i=\frac{525}{2}, \] then $\sum_{i=1}^{17} a_i$ is equal to