【题目链接】
【思路要点】
- 补档博客,无题解。
【代码】
#include<bits/stdc++.h> using namespace std; #define MAXN 100005 template <typename T> void read(T &x) { x = 0; int f = 1; char c = getchar(); for (; !isdigit(c); c = getchar()) if (c == '-') f = -f; for (; isdigit(c); c = getchar()) x = x * 10 + c - '0'; x *= f; } int tot, prime[MAXN]; int f[MAXN], miu[MAXN]; void init() { miu[1] = 1; for (int i = 2; i < MAXN; i++) { if (f[i] == 0) { f[i] = prime[++tot] = i; miu[i] = -1; } for (int j = 1; j <= tot && prime[j] <= f[i]; j++) { int tmp = prime[j] * i; if (tmp >= MAXN) break; f[tmp] = prime[j]; if (prime[j] == f[i]) miu[tmp] = 0; else miu[tmp] = -miu[i]; } } } int main() { init(); long long n, m; read(n), read(m); if (n > m) swap(n, m); long long ans = 0; for (int i = 1; i <= n; i++) for (int j = 1; i * j <= n; j++) ans += i * miu[j] * (n / i / j) * (m / i / j); cout << ans * 2 - n * m << endl; return 0; }