大白书P125
1 #include <iostream> 2 #include <cstring> 3 using namespace std; 4 #define MMX 4000010 5 #define LL long long 6 int phi[MMX],f[MMX]; 7 LL S[MMX]; 8 9 void calc_phi(int n) //求1--n的欧拉函数,phi[i]=φ(i) 10 { 11 for (int i=2;i<=n;i++) 12 phi[i]=0; 13 phi[1]=1; 14 for (int i=2;i<=n;i++) 15 if (!phi[i]) 16 for (int j=i;j<=n;j+=i) 17 { 18 if (!phi[j]) phi[j]=j; 19 phi[j]=phi[j]/i*(i-1); 20 } 21 } 22 23 int main() 24 { 25 calc_phi(MMX); 26 memset(f,0,sizeof(f)); 27 for (int i=1;i<=MMX;i++) 28 for (int j=2*i;j<=MMX;j+=i) 29 f[j]+=i*phi[j/i]; 30 31 S[2]=f[2]; 32 for (int i=3;i<=MMX;i++) 33 S[i]=S[i-1]+f[i]; 34 35 int n; 36 while (cin>>n) 37 { 38 if (n==0) break; 39 cout<<S[n]<<endl; 40 } 41 }
时间: 2024-10-13 01:11:11