e_0 = n,
　e_1 = n+1,
　e_2 = n(n+1) + 1,
　e_3 = n(n+1){n(n+1)+1} + 1,
とおくと
　1/e_0 − 1/e_1 − 1/e_2 − 1/e_3 = 1/(e_0･e_1･e_2･e_3),

数学セミナー, vol.50, no.3 (2011/Mar)
　NOTE　　p.67-68