题目链接
一个数论分块 一个等差数列 数论分开的板子一直记得是个错的 妈蛋 记得加mod 因为 等差数列是递减的 我一直以为是越界 int128都上了
#include <bits/stdc++.h> using namespace std; const int mod = 1e9+ 7; #define int long long typedef long long ll; typedef __int128 LL; ll quick(ll a, ll b){ ll ans = 1; while(b){ if(b&1){ ans = ans*a%mod; } b >>= 1; a = a*a%mod; } return ans; } signed main() { int n; cin >> n; LL ans = 0; int inv = quick(2, mod - 2); for(int i = 1; i <= n ;){ LL len = n/(n/i); LL len1 = (len - i + 1); len1%= mod; ans = (ans + (len1*(n%i)%mod + len1*(len1 - 1)%mod*(-1*(n/i))%mod*inv%mod)%mod)%mod; i = len + 1; } ll ans1 = ans; cout << ans1 << endl; }