因为an - an-1 = (2n-1) - (2n-3) = 2
此为等差级数:
以首项:a1 = 1,末项:an = 2n-1,项数:n
1+3+5+7+9+、、、、、、+2n-3+2n-1的值:n/2 (a1+an)
= n/2 (1+2n-1)
= n^2