Prime visits test case 1 is failing

#1

#include
using namespace std;
int main() {
int t;
cin>>t;
while(t>0)
{
int u=0;
int a,b;
cin>>a>>b;
int c=a;
while(c<=b)
{
int j=2;
if(c<=3)
{u=2;
}
while(j<=c/2)
{
if (c%j==0)
{
break;
}
else if(j==c/2)
{
u=u+1;
break;
}
j=j+1;
}
c=c+1;
}
cout<<u<<endl;
t=t-1;
}
return 0;
}

#2

Find all the prime numbers using seive of erathones and then check with each pair whether their multiplicaiton is within the range or not. In this way you will only be enumerating the prime numbers which are very less comparable to the range itself.

#3

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