uva 10820 约束个数

#include <bits/stdc++.h>using namespace std;const int maxn = 5E4 + 10;int f[maxn], phi[maxn] = {0, 1}, n;void init(){for (int i = 2; i < maxn; i++){if (phi[i]) continue;for (int j = i; j < maxn; j += i){if (!phi[j]) phi[j] = j;phi[j] = phi[j] / i * (i - 1);}}for (int i = 2; i < maxn; i++)f[i] = f[i - 1] + phi[i];}int main(int argc, char const *argv[]){init();while (cin >> n && n)cout << 2 * f[n] + 1 << endl;return 0;}

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