Find primes in numbers
// Find primes in numbers
fn prime_factors(n: i64) -> String {
  let mut n = n as u64;
  let mut d = 2;
  let mut mem = std::collections::BTreeMap::new();
  while d <= n {
    if n % d == 0 {
      n /= d;
      let old = mem.entry(d).or_insert(0);
      *old += 1;
    } else {
      d += 1;
    }
  }
  mem.iter().map(|(key, val)| match *val {
    1 => format!("({})", key),
    _ => format!("({}**{})", key, val),
  }).collect::<String>()
}
fn main() {
    println!("Primes in numbers = {} ", prime_factors(7775460));
    println!("Primes in numbers = {} ", prime_factors(13*17*3*26));
    println!("Primes in numbers = {} ", prime_factors(14));
}
