Cho S = 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42. So sánh S với 1

S=12+16+112+120+130+142=11.2+12.3+13.4+14.5+15.6+16.7=1−12+12−13+13−14+14−15+15−16+16−17=1−17<1

So sánh: S < 1.