Compute the nth prime number

fn nth(n: u32) -> u32 {
    let mut primes = Vec::new();
    let mut i = 2;
    while primes.len() < n as usize {
        if is_prime(i) {
            primes.push(i);
        }
        i += 1;
    }
    *primes.last().unwrap()
}