hdu 2824 The Euler function（欧拉函数）

The Euler function

[b]Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)

Total Submission(s): 3004 Accepted Submission(s): 1230

[/b]

Problem Description

The Euler function phi is an important kind of function in number theory, (n) represents the amount of the numbers which are smaller than n and coprime to n, and this function has a lot of beautiful characteristics. Here comes a very easy question: suppose
you are given a, b, try to calculate (a)+ (a+1)+....+ (b)

Input

There are several test cases. Each line has two integers a, b (2<a<b<3000000).

Output

Output the result of (a)+ (a+1)+....+ (b)

Sample Input

3 100

Sample Output

3042

Source

2009 Multi-University Training
Contest 1 - Host by TJU

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gaojie

题意：求那个式子啊..
题解：先把欧拉函数的表用筛素数的方法搞出来

#include<stdio.h>
#include<string.h>
#define inf 3000000
long long f[inf+5];
void div()
{
int i,j;
memset(f,0,sizeof(f));
f[0]=0;  f[1]=1;
for(i=2; i<=inf; i++)
{
if(!f[i])
{
for(j=i; j<=inf; j+=i)
{
if(!f[j]) f[j]=j;
f[j]=f[j]/i*(i-1);
}
}
f[i]+=f[i-1];
}
}
int main()
{
int a,b;

div();
while(scanf("%d%d",&a,&b)>0)
{
if(a>b) a^=b^=a^=b;
printf("%I64d\n",f[b]-f[a-1]);
}

return 0;
}