loj125 除数函数求和 2

https://loj.ac/problem/125

$原式=2\sum_{i=1}^n(i^2*{\lfloor}{\frac{n}{i}}{\rfloor})+3\sum_{i=1}^n(i*{\lfloor}{\frac{n}{i}}{\rfloor})+5\sum_{i=1}^n({\lfloor}{\frac{n}{i}}{\rfloor})$

 #include<cstdio>
 #include<algorithm>
 #include<cstring>
 #include<vector>
 using namespace std;
 #define fi first
 #define se second
 #define mp make_pair
 #define pb push_back
 typedef long long ll;
 typedef unsigned long long ull;
 typedef pair<int,int> pii;
 #define md 998244353
 ll n,a1,a2,a3;
 ll calc(ll x)    {return x*(x+)%md*(*x+)%md*%md;}
 int main()
 {
     ll i,j,t;
     scanf("%lld",&n);
     for(i=;i<=n;i=j+)
     {
         t=n/i;
         j=min(n,n/t);
         a1=(a1+(calc(j)-calc(i-)+md)%md*t%md)%md;
         a2=(a2+(i+j)*(j-i+)%md*%md*t%md)%md;
         a3=(a3+(j-i+)*t)%md;
     }
     printf("%lld",(*a1+*a2+*a3)%md);
     return ;
 }