iskander's questions

通过变量计算函数的值：

Pestiferous (n)
       r = 0;
       for i = 1 to n do
           for j = 1 to i do
               for k = j to i + j do
                   for l = 1 to i + j - k do
                           r = r + 1;
       return (r)

我尝试计算总和，得到r = n(n + 1)(n + 2)(n + 3) / 24，但答案没有通过计算机检查。