per/src/main.rs

extern crate num_bigint;
// extern crate num_traits;

use num_bigint::BigUint;


fn main()
{
    let mut num = BigUint::from(0 as u8);
    num = num + 277777788888899u128;

    println!("{:?}", test(num));
}

fn test(input: BigUint) -> u8 {
    let mut n = factorize(input);
    let mut counter = 1;
    while (n.to_str_radix(10).chars().count() > 1) {
        n = factorize(n);
        println!("n: {:?}", n);
        counter += 1;
    }
    return counter;
}

fn factorize(input: BigUint) -> BigUint {
    let string = input.to_str_radix(10);
    let numbers: Vec<u8> = string.chars().map(|x| x as u8 - 48).collect();
    numbers.into_iter().product::<BigUint>()
}