וּבְנֵ֖י חֶלְאָ֑ה צֶ֥רֶת יצחר [וְצֹ֖חַר] וְאֶתְנָֽן׃
And the sons of Helah were Zereth, and Zohar, and Ethnan.
Rashi
And Reaiah This is the manner in which this genealogy [is written]; although Reaiah, [and his father] were not enumerated above, [he is mentioned here] because the Chronicler reckons [only] certain generations. Likewise, (vs. 7f.): “And the sons of Helah: Zereth, and Zohar, and Ethnan. And Koz begot...” Although he did not yet mention Koz, he mentions his sons.