We pick h.root-servers.net, one of the 13 root servers (1), and ask it about ns4.showhaber.org and learn that org is delegated to six name servers (2), so we ask a0.org.afilias-nst.info where we learn that showhaber.org is delegated to four name servers, including ns3.showhaber.org (3), so we ask that one and get the following answer:
All of the four domains that use the primary name server ns2.showhaber.org use name server group 1. Worth noting is that four of the domains that use name server group 1 use the primary name server ns2.showhaber.org.
The two name servers ns1 and ns2.showhaber.org together
There are twelve domains that use name server group 1.
Seven of those are under the tld "org".
Five of them are under the tld "com".
Four of them use the primary name server ns2.showhaber.org. Worth noting is that all of the domains that use the primary name server ns2.showhaber.org use name server group 1.