'Firstborn Son' in the Bible

“If a man has two wives, one loved and the other unloved, and both the loved and the unloved have born him sons, and the firstborn son belongs to the unloved wife,

It shall be that her firstborn [son] will be given the name of the dead brother, so that his name will not be blotted out of Israel.

and his firstborn son was Abdon, then Zur, Kish, Baal, Nadab,

and his firstborn son was Abdon, then Zur, Kish, Baal, Ner, Nadab,