Er and Onan were sons of Judah, but they died in Canaan.
Read Numbers 26:19 Using Other Translations
The sons of Judah were Er and Onan: and Er and Onan died in the land of Canaan.
The sons of Judah were Er and Onan; and Er and Onan died in the land of Canaan.
Judah had two sons, Er and Onan, who had died in the land of Canaan.
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(New International Version Bible Online)