数列求和

0
lzx_yyds_2015 LV 3 @ 2026-4-3 7:36:56

#include<bits/stdc++.h> using namespace std; int n,a[100005]={1},s; int main(){ cin>>n; for(int i = 1;i<=n;i++){ a[i]=a[i-1]-1+i; s+=a[i]; } cout<<s; return 0; }
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zhangxin LV 6 @ 2026-4-1 13:21:51

#include<bits/stdc++.h> using namespace std; int n,a[100005]={1},s; int main(){ cin>>n; for(int i = 1;i<=n;i++){ a[i]=a[i-1]-1+i; s+=a[i]; } cout<<s; return 0; }
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zhengkaiyang666 LV 8 @ 2026-3-31 16:56:26

#include<bits/stdc++.h> using namespace std; int n; int main(){ cin>>n; long long sum=(long long)n*(n*n+5)/6; cout<<sum; return 0; }