Depends very much on what exactly you need. Up to 2^64-1 leading zeros followed by as high as you like (the RAM is the limit) positive value? struct Number

Depends very much on what exactly you need. Up to 2^64-1 leading zeros followed by as high as you like (the RAM is the limit) positive value? struct NumberWithLeadingZeros { leading_zeros: u64, number: Vec<u64> } Then implement some traits for it add, sub, pow, to_string etc. and work with it. Or do something else that fits exactly your needs.