24 Because vengeance has been exacted seven times on Cain's behalf, on Lamech's [it shall be] seventy times seven.
Genesis 4:24 Cross References - LXX2012
Genesis 4:15
15 And the Lord God said to him, Not so, any one that slays Cain shall suffer sevenfold vengeance; and the Lord God set a mark upon Cain that no one that found him might kill him.