501

t.rs

struct Primes {
    primes : Vec<u64>,
}
impl Primes {
    fn new() -> Primes {
        Primes{primes: vec![2]}
    }
    
    fn test(&self, totest: u64) -> bool {
        let mut n = totest;
        for &i in &self.primes {
            while n%i == 0 {n /= i;}
            if n==1 {return false;}
        }
        return true;
    }
}

impl Iterator for Primes {
    type Item = u64;

    fn next(&mut self) -> Option<u64> {
        let mut n = *self.primes.last().unwrap() + 1;
        while !self.test(n) { n += 1; }
        self.primes.push(n);
        return Some(n);
    }
}

fn testnum (primes: &Vec<u64>, i: u64) -> u64 {
    let mut k = i;
    let mut count = 0;
    for &prime in primes {
        while k%prime == 0 {
            k /= prime;
            count += 1;
            if count == 4 && k==1 {return 1}
            else if count > 4 || k==1 {return 0}
        }
    }
    if count == 4 && k==1 {1} else {0}
}

fn main() {
    let m = 100u64;
    let primes : Vec<u64> = Primes::new().take(m).collect();
    
    let mut s = 0;
    for i in 1..m {
        s += testnum(&primes, i);
    }
    println!("{}", s);
}