וַיְחִ֣י קֵינָ֗ן אַחֲרֵי֙ הוֹלִיד֣וֹ אֶת־מַֽהֲלַלְאֵ֔ל אַרְבָּעִ֣ים שָׁנָ֔ה וּשְׁמֹנֶ֥ה מֵא֖וֹת שָׁנָ֑ה וַיּ֥וֹלֶד בָּנִ֖ים וּבָנֽוֹת׃
And Kenan lived after he begot Mahalalel eight hundred and forty years, and begot sons and daughters.
Read midrashic interpretation of Genesis 5:13: and classical rabbinic exegesis.