7/6 + 13/12 + 21/21 + 31/30 + 43/42 + 57/56 + 73/72 + 91/90 =[(2*3+1)/2*3]+[(3*4+1)/3*4]+[(4*5+1)/4*5]+[(5*6+1)/5*6]+[(6*7+1)/6*7]+...=1+1/2*3+1+1/3*4...=8+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7+...=8+1/2-1/3+...