How can we calculate this sum: [math]\sum_{i = 0}^{n-2}\sum_{j=i}^{n}(i + j) + \sum_{i = 0}^{n-2}\sum_{j=i}^{n}1[/math]?
How do you find the sum[math] \displaystyle\sum_{i=0}^{n} (n(n+1))^{2(n+2)}[/math]