Implementation of https://xkcd.com/2835/
https://crates.io/crates/variable_base_factoradic
cargo install variable_base_factoradic
use variable_base_factoradic::VariableBaseFactoradicNumber;
// Convert from decimal to factoradic
let v = VariableBaseFactoradicNumber::try_new(5038).unwrap();
println!("{}", v.to_string()); // 654320
// Convert from factoradic to decimal
let v = "654320".parse::<VariableBaseFactoradicNumber>().unwrap();
println!("{}", v.value); // 5038