It is the number that identifies each member institution at Crossref. It is used, for instance, to access the member Participation Report.
Enter the DOI prefix (e.g. 10.58976) and the tool returns the owning institution and its member ID, with a direct link to the participation report.
A public Crossref dashboard showing the completeness of the metadata deposited by the member: abstracts, ORCID, references, licenses and other indicators.