1/20+1/30+1/42+.+1/132+1/156=1/4-1/5+1/5-1/6+1/6-1/7+...-1/12+1/12-1/13=1/4-1/13=9/52（裂项相消）
1-1/2-1/4-1/8-1/16-1/32-.1/1024=1-（1/2+1/4+1/8+1/16+...+1/1024）=1-1/2[1-（1/2）^10]/(1-1/2)=1-(1-1/1024)=1/1024
2+3 1/6+5 1/12+7 1/20+11 1/30+13 1/42=2+3+5+7+11+13+1/6+1/12+1/20+1/30+1/42=41+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7=41+1/2-1/7=41 5/14(还是裂项相消)