UVa 10820 (打表、欧拉函数) Send a Table

 1 #include <cstdio>
 2 
 3 const int maxn = 50000;
 4 
 5 int phi[maxn + 10], sum[maxn + 10];
 6 
 7 void phi_table(int n)
 8 {
 9     phi[1] = 0;
10     for(int i = 2; i <= maxn; ++i) if(!phi[i]) //说明i为素数
11     {
12         for(int j = i; j <= maxn; j += i)
13         {
14             if(!phi[j]) phi[j] = j;
15             phi[j] = phi[j] / i * (i - 1);
16         }
17     }
18 }
19 
20 int main()
21 {
22     phi_table(maxn);
23     sum[1] = phi[1];
24     for(int i = 2; i <= maxn; ++i) sum[i] = sum[i - 1] + phi[i];
25     
26     int n;
27     while(scanf("%d", &n) == 1 && n) printf("%d\n", 2*sum[n]+1);
28     
29     return 0;
30 }