Hi Sarah,
Each number represent mapping of id for the node.
For example in your case,
/browser/<node>/children/<server-group-id>/<server-id>
/browser/server/children/1/3
Here <node> is the type of object (eg: server-group, server, database, table etc) and <server-id> will be the column 'id' of server table(pgadmin4.db), I guess you have multiple entries of a same server with different name in sqltite database.
/browser/<node>/children/<server-group-id>/<server-id>/<database-id>
/browser/database/children/1/1/12641
Here <database-id> is OID of connected database.
We follow this same URL object mapping almost everywhere in pgAdmin4.