17/11/28 23:24:09.55 8oBcz/rm.net
>>183
Σ[a=1,27] Σ[b=a+1,28] Σ[c=b+1,29] Σ[d=c+1,30] Σ[e=d+1,31] (a+b+c+d+e)
= Σ[a=1,27] Σ[b=a+1,28] Σ｢c=b+1,29] Σ[d=c+1,30] (1/2)(31-d)(32+2a+2b+2c+3d)
= Σ[a=1,27] Σ[b=a+1,28] Σ[c=b+1,29] (1/2)(30-c)(31-c)(32+a+b+2c)
= Σ[a=1,27] Σ[b=a+1,28] (1/4)(29-b)(30-b)(31-b){32+(2a+5b)/3}
= Σ[a=1,27] (1/12)(28-a)(29-a)(30-a)(31-a)(32+3a/2)
= 27*28*29*30*31*(2/3)
= 80 C[31,5]
= 13592880.