John Gill Commentary Numbers 26:42

"These are the sons of Dan after their families: of Shuham, the family of the Shuhamites. These are the families of Dan after their families." — Numbers 26:42 (ASV)

Ver. 42,43. These are the sons of Dan, after their families

Though he had but one son, the plural being put for the singular; or by sons are meant his posterity; his son's name was Shuham, and by transposition Hushim, in (Genesis 46:23) from him was the family of the Shulamite; and yet, though but one, consisted of 64,400 men; there was an increase of 1700 in this tribe.