HDU 2841 Visible Trees

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<queue>
#include<set>
#include<map>
#include<cstring>
#include<vector>
using namespace std;
class Node
{
public:
int cnt,num[20];
}node[100024];
void Prime( )
{
int prime[10000],cnt=0;
bool hash[50024]={0};
int t = (int)sqrt( 100000.0 ) + 1;
for( int i = 3 ; i <=t ; i+=2 )
{
if( !hash[i>>1] )
{
int x = i<<1;
for( int j = i * i ; j <=100001; j += x )
hash[j>>1] = true;
}
}
prime[cnt++] = 2;
for( int i = 1 ;i <= 50000 ; i++ )
{
if( !hash[i] )
{
prime[cnt++] = ( i << 1 ) + 1;
}
}
for( int i = 2; i <= 100000 ; i++ )
{
t = i;
node[i].cnt = 0;
for( int j = 0 ; j < cnt; j ++ )
{
if( prime[j] > t ) break;
if( t % prime[j] == 0 )
{
node[i].num[node[i].cnt++] = prime[j];
while( t % prime[j] == 0 )
t /= prime[j];
}
}
}
}
long long DFS( int t , int m , int k )
{
long long ans = 0;
for( int i = t ; i < node[k].cnt ;i ++ )
{
ans += m/node[k].num[i] - DFS( i + 1 , m/node[k].num[i] , k );
}
return ans;
}
int main(  )
{
int n ,m,Case;
Prime();
while( scanf( "%d\n",&Case ) ==1 )
{
while( Case-- )
{
long long ans = 0;
scanf( "%d %d",&n,&m );
for( int i = 1; i <= n ; i++ )
ans += m - DFS( 0 , m , i );
printf( "%I64d\n",ans );
}
}
//system( "pause" );
return 0;
}