'commit'

TangDou/AcWing_TiGao/T5/RongChi/HDU3501_Euler.cpp

@@ -0,0 +1,26 @@
+#include <bits/stdc++.h>
+using namespace std;
+typedef unsigned long long ULL;
+const ULL mod = 1000000007;
+
+ULL euler(ULL n) {
+    ULL res = n, a = n;
+    for (ULL i = 2; i * i <= a; i++) {
+        if (a % i == 0) {
+            res = res / i * (i - 1);
+            while (a % i == 0) a /= i;
+        }
+    }
+    if (a > 1) res = res / a * (a - 1);
+    return res;
+}
+
+int main() {
+    ULL n;
+    while (~scanf("%llu", &n), n) {
+        ULL sum = n * (1 + n) / 2 - n, ans;
+        ans = sum - euler(n) * n / 2;
+        printf("%llu\n", ans % mod);
+    }
+    return 0;
+}