3:17 These were the sons of Levi by their names: Gershon, Kohath, and Merari.
3:18 These are the names of the sons of Gershon by their families: Libni and Shimei.
3:19 The sons of Kohath by their families were: Amram, Izhar, Hebron, and Uzziel.
Numbers 8:18
8:18 So I have taken the Levites instead of all the firstborn sons among the Israelites.