1/（1×3×5）+1/（3×5×7）+1/（5×7×9）＋1／（7×9×11）＋1／（9×11×13）=(1/2)*[1/(1*3)-1/(3*5)]+(1/2)*[1/(3*5)-1/(5*7)]+...+(1/2)*[1/(9*11)-1/(11*13)]=(1/2)*[1/(1*3)-1/(11*13)]=(1/2)*(140/429)=70...