Probably Peano numbers.

https://wiki.haskell.org/Peano_numbers

>Succ Peano

...

The standard joke about my university's grad-level programming languages course is that its formalization unit does a great job of identifying undergrads by discussing Peano naturals and Hoare logic in the same lecture...

Perhaps Nock:

https://developers.urbit.org/reference/nock/definition

> The reader might wonder how an interpreter whose only arithmetic operation is increment can ever be practical.

> The short answer is that a Nock interpreter doesn't have to use the algorithm above. It just has to get the same result as the algorithm above.