12.2.4 Number theory

Problem: One stone was put in each of the points \( n \) with the cooridinates \( x=1, x=2, \ldots, x=n \) in ascending order of their weight. The weight of the lightest stone is \( 3 \mathrm{~kg} \). The weight of each next stone is \( 1 \mathrm{~kg} \) less, than the twice weight of the previous one. Find the total weight of the first 10 stones. For what \( n(9