import std.algorithm;
import std.array;
import std.ascii;
import std.bigint;
import std.complex;
import std.container;
import std.conv;
import std.functional;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

auto readInts() {
	return array(map!(to!int)(readln().strip().split()));
}
auto readInt() {
	return readInts()[0];
}
auto readLongs() {
	return array(map!(to!long)(readln().strip().split()));
}
auto readLong() {
	return readLongs()[0];
}

void readlnTo(T...)(ref T t) {
    auto s = readln().split();
    assert(s.length == t.length);
    foreach(ref ti; t) {
        ti = s[0].to!(typeof(ti));
        s = s[1..$];
    }
}

const real eps = 1e-10;

void main(){
    auto isPrime = new bool[](1000000);
    isPrime.fill(true);
    isPrime[0] = false;
    isPrime[1] = false;
    foreach(i; iota(isPrime.length)) {
        if(isPrime[i]) {
            auto j = i*2;
            while(j < isPrime.length) {
                isPrime[j] = false;
                j += i;
            }
        }
    }
    auto primes = zip(isPrime, iota(isPrime.length)).filter!(a => a[0]).map!(a => a[1].to!int).array.assumeSorted;
    while(true) {
        auto n = readInt();
        if(n == 0) {
            return;
        }
        int ans;
        foreach(i; iota(n)) {
            int p, m;
            readlnTo(p, m);
            auto x = primes.upperBound(p-m-1).lowerBound(p+m+1).length;
            ans += x-1;
        }
        writeln(ans);
    }
}