As for the sons of Merari, you are to number them by their clans and families,

Numbers 4:28
This is the service of the Gershonite clans at the Tent of Meeting, and their duties shall be under the direction of Ithamar son of Aaron the priest.

Numbers 4:30
from thirty to fifty years old, counting everyone who comes to serve in the work of the Tent of Meeting.

As for the sons of Merari, you shall number them after their families, by the house of their fathers;