要求这个级数的总和，我们首先分析这个级数。
该级数是：2,6,12,20,30…
示例
For n = 6 Sum = 112 On analysis, (1+1),(2+4),(3+9),(4+16)... (1+1<sup>2</sup>), (2+2<sup>2</sup>), (3+3<sup>2</sup>), (4+4<sup>2</sup>), can be divided into two series i.e. s1:1,2,3,4,5… andS2: 1<sup>2</sup>,<sup>2</sup>,3<sup>2</sup>,....
使用数学公式求出第一个和第二个之和
Sum1 = 1+2+3+4… , sum1 = n*(n+1)/2 Sum2 = 12+2<sup>2</sup>+3<sup>2</sup>+4<sup>2</sup>… , sum1 = n*(n+1)*(2*n +1)/6
示例
#include <stdio.h>
int main() {
int n = 3;
int sum = ((n*(n+1))/2)+((n*(n+1)*(2*n+1))/6);
printf("the sum series till %d is %d", n,sum);
return 0;
}输出
The sum of series till 3 is 20
