Midrasch zu Schemot 6:16

Rabbi Elazar, son of 'Azariah, said: Is it not so that the Israelites did not dwell in Egypt except for 210 years? But in order to teach thee, know that this is so, come and see; for when Joseph went down to Egypt he was seventeen years old, and when he stood before Pharaoh he was thirty years old, as it is said, "And Joseph was thirty years old when he stood before Pharaoh, king of Egypt" (Gen. 41:46). And the seven years of plenty, and the two years of famine, behold, they are nine-and-thirty years (in all). And Levi, the son of Jacob, was six years older than Joseph, and when he went down to Egypt he was forty-five years, and the years of his life in Egypt were ninety-two years; behold, all of them (amount to) 137 years, (as it is said,) "And the years of the life of Levi were an hundred thirty and seven years" (Ex. 6:16). On his going down to Egypt, his wife bare unto him Jochebed, his daughter, as it is said, "And the name of Amram's wife was Jochebed" (Num. 26:59), and she was 130 years when she bare Moses, (as it is said,) "And Moses was fourscore years old when he stood before Pharaoh" (Ex. 7:7). || Behold, (the total is) 210 years in all. And thus it says, "And they shall serve them; and they shall afflict them four hundred years" (Gen. 15:18).