Problem:
Score : 400 points

Problem Statement

We say that a odd number N is similar to 2017 when both N and (N+1)/2 are prime.

You are given Q queries.

In the i-th query, given two odd numbers l_i and r_i, find the number of odd numbers x similar to 2017 such that l_i ≤ x ≤ r_i.

Constraints

1≤Q≤10^5

1≤l_i≤r_i≤10^5

l_i and r_i are odd.

All input values are integers.

Input

Input is given from Standard Input in the following format:

Q
l_1 r_1
:
l_Q r_Q

Output

Print Q lines. The i-th line (1≤i≤Q) should contain the response to the i-th query.

Sample Input 1

1
3 7

Sample Output 1

2

3 is similar to 2017, since both 3 and (3+1)/2=2 are prime.

5 is similar to 2017, since both 5 and (5+1)/2=3 are prime.

7 is not similar to 2017, since (7+1)/2=4 is not prime, although 7 is prime.

Thus, the response to the first query should be 2.

Sample Input 2

4
13 13
7 11
7 11
2017 2017

Sample Output 2

1
0
0
1

Note that 2017 is also similar to 2017.

Sample Input 3

6
1 53
13 91
37 55
19 51
73 91
13 49

Sample Output 3

4
4
1
1
1
2

Solution in Rust (1.15.1) (judge verdict: Accepted)

fn main() {
    let q = read::<u32>();
    let v = read_vec2::<usize>(q);
    let mut arr = [0;100001];
    let mut count = 0;
    arr[1] = 0;
    for i in 3..100001 {
        if i % 2 == 0 { continue; }
        if is_prime(i) && is_prime((i+1)/2) {
            count += 1;
        }
        arr[i as usize] = count;
    }

    for v in v {
        let l = v[0] as usize;
        let r = v[1] as usize;
        if l > 1 && arr[l] > arr[l-2] {
            println!("{}", arr[r]-arr[l]+1);
        } else {
            println!("{}", arr[r]-arr[l]);
        }
    }
}

fn is_prime(n:u32) -> bool {
    if n == 1 { return false; }
    let mx = (n as f64).sqrt().floor() as u32 + 1;
    for i in 2..mx {
        if n%i==0 {
            return false;
        }
    }
    true
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>().split_whitespace()
        .map(|e| e.parse().ok().unwrap()).collect()
}

fn read_vec2<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}