#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <deque>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
#include <cctype>
#include <cstring>
#include <ctime>
#include <iterator>
#include <bitset>
#include <numeric>
#include <list>
#include <iomanip>

#if __cplusplus >= 201103L
#include <array>
#include <tuple>
#include <initializer_list>
#include <unordered_set>
#include <unordered_map>
#include <forward_list>

#define cauto const auto&
#else

#endif

using namespace std;


namespace{
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef vector<int> vint;
typedef vector<vector<int> > vvint;
typedef vector<long long> vll, vLL;
typedef vector<vector<long long> > vvll, vvLL;

#define VV(T) vector<vector< T > >

template <class T>
void initvv(vector<vector<T> > &v, int a, int b, const T &t = T()){
    v.assign(a, vector<T>(b, t));
}

template <class F, class T>
void convert(const F &f, T &t){
    stringstream ss;
    ss << f;
    ss >> t;
}


#define reep(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) reep((i),0,(n))
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define F first
#define S second
#define mkp make_pair
#define RALL(v) (v).rbegin(),(v).rend()


#define MOD 1000000007LL
#define EPS 1e-8
static const int INF=1<<24;

const int maxn=1000010;
int f[maxn],prime[maxn];
 
int GenP() {
	int i,tot,p,tmp;
	tot=0;
	for (i=2;i<maxn;++i) f[i]=i;
	for (p=2;p<maxn;++p)
	{
		if (f[p]==p) prime[tot++]=p;
		for (i=0;i<tot && prime[i]<=f[p];++i)
		{
			tmp=prime[i]*p;
			if (tmp<maxn) 
				f[tmp]=prime[i];
			else
				break;
		}
	}
}
int a[1000010];
void mainmain(){
	GenP();
	int t=0;
	reep(i,1,1000010){
		a[i]=a[i-1];
		if(prime[t]==i){
			t++;
			a[i]++;
		}
	}
	int n;
	while(cin>>n,n){
		int ans=0;
		rep(i,n){
			int p,m;
			cin>>p>>m;
			int x=p-m,y=p+m;
			if(x<1) x=1;
			if(y>1000000) y=1000000;
			ans+=a[y]-a[x-1]-1;
		}
		cout<<ans<<endl;
	}
}



}
main() try{
    mainmain();
}
catch(...){
}