1/3看做1/(2×1+1) 1/15看做(1/3)×(1/5)即1/(2×1+1) 和 1/(2×2+1) 的乘积 以此类推
Sn=1/(2×1+1) + 1/(2×1+1) 1/(2×2+1) + 1/(2×2+1)*[1/(2×3+1)] + 1/(2×3+1)*[1/(2×4+1)] + 1/(2×4+1)*[1/(2×5+1)] +.+ 1/(2×n+1)*[1/(2×(n+1)+1) ]
这个算数n=5
S5=(n+1)/[2(n+1)+1]
=(5+1)/[2*(5+1)+1]
=6/13