fn sum_of_divisors(val: u32) -> u32 {
    (1..val/2+1).filter(|n| val % n == 0)
                .fold(0, |sum, n| sum + n)
}

fn main() {
    let iter = (1..20_000).map(|i| (i, sum_of_divisors(i)))
                          .filter(|&(i, div_sum)| i > div_sum);

    for (i, sum1) in iter {
        if sum_of_divisors(sum1) == i {
           println!("{} {}", i, sum1);
        }
    }
}