c语言数列求第n项及前n项和

Question

Answer 1

#include<cstdio>
int main()
{
    int n;
    scanf("%d",&n);
    int f1 = 1,f2 = 1,f,sum = 2;
    for(int i = 3;i <=n ;i++){
        f = 3 * f2 + 2 * f1;
        sum += f;
        f1 = f2;
        f2 = f;
    }
    printf("%d %d",f,sum);
    
    
    return 0;
}