There is a math problem n+3 (n-1)+5 (n-2)+...+(2n-1)1=? Ask the solution of this set of questions, and ask the problem-solving skills of "arithmetic × arithmetic".
Let Sn = n+3 (n-1)+5 (n-2)+...+(2n-1), so Sn-1= (n-1)+3 (n-2)+
This kind of problem can be recreated as a series of numbers. Subtract the two types to find their laws, and then sum them up to work out the answer!