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37 lines
764 B
37 lines
764 B
#include <bits/stdc++.h>
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using namespace std;
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#define int long long
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#define endl "\n"
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const int MOD = 1e9 + 7;
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/*
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3
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4
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0
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答案
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0
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2
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*/
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// 求单个数值的欧拉函数值
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int phi(int x) {
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int res = x;
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for (int i = 2; i <= x / i; i++) {
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if (x % i == 0) {
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res = res / i * (i - 1);
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while (x % i == 0) x /= i;
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}
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}
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if (x > 1) res = res / x * (x - 1);
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return res;
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}
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signed main() {
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int n;
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while (cin >> n && n) {
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// 小于n的数字中有多少个数字与n互质
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int ans = n * (n - 1) / 2; // 高斯公式，(首页+末项)*项数/2
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ans = (ans - phi(n) * n / 2) % MOD; // 扣除掉 phi(n)*n/2
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cout << ans << endl;
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}
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}
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