libmumps-seq-dev binary package in Ubuntu Focal amd64

 MUMPS implements a direct solver for large sparse linear systems, with a
 particular focus on symmetric positive definite matrices. It can
 operate on distributed matrices e.g. over a cluster. It has Fortran and
 C interfaces, and can interface with ordering tools such as Scotch.
 .
 This package is built the MUMPS libseq dummy sequential MPI library.
 Unless you know that you specifically need this, then you almost
 certainly want the libmumps-dev package.

Source package