题解 | many sum

#include <bits/stdc++.h>
using namespace std;
const int N=2e6+10;
const int mod = 998244353;
typedef long long ll;
typedef unsigned long long ull;
int n,a1,m;
int a[N];
ll b[N];
void solve()
{
    cin>>n>>a[1]>>m;

    for(int i=2;i<=n;i++)
    {
        a[i] = (a[i-1]+7*i)%m;
    }
    int ans = 0;

    for(int i=1;i<=n;i++)
    {
        for(int j=i;j<=n;j+=i)
        {
            b[j]+=a[i];
        }
    }

    for(int i=1;i<=n;i++)
    {
        ans ^= b[i];
    }
    cout<<ans<<'\n';
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t=1;
    // cin>>t;
    while(t--)
    {
        solve();

    }


    return 0;
}

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