Question Number 194610 by justenspi last updated on 11/Jul/23

Answered by qaz last updated on 11/Jul/23
 =[1≤k≤n][i+1≤j≤k−1][1≤i≤j−1](i+j+k) =[3≤k≤n][2≤j≤k−1][1≤i≤j−1](i+j+k) =[3≤k≤n][2≤j≤k−1]((1/2)j(j−1)+(j−1)(j+k)) =[3≤k≤n](k^3 −3k^2 +2k) =(1/4)(n−2)(n−1)n(n+1) ,(n∈N , n≥3)](https://www.tinkutara.com/question/Q194621.png)
Commented by justenspi last updated on 11/Jul/23

Commented by qaz last updated on 11/Jul/23

Commented by justenspi last updated on 11/Jul/23
