1/2 + 1/6 + 1/12 + 1/20+ 1/30 + 1/42= 1 - 1/2 + 1/2 - 1/3+ 1/3 - 1/4 + 1/4 - 1/5+ 1/5 - 1/6 + 1/6 - 1/7= 1 - 1/7= 6/7
219/113
