libnum-ocaml-dev binary package in Ubuntu Focal amd64

 This OCaml library implements arbitrary-precision arithmetic on big
 integers and on rationals.
 .
 This is a legacy library. It used to be part of the core OCaml
 distribution (in otherlibs/num) but is now distributed separately. New
 applications that need arbitrary-precision arithmetic should use the
 Zarith library (https://github.com/ocaml/Zarith) instead of the Num
 library, and older applications that already use Num are encouraged to
 switch to Zarith. Zarith delivers much better performance than Num and
 has a nicer API.
 .
 This package contains development files.

Source package