'Seventy' in the Bible

Now there were in Samaria seventy of Ahab's sons. And Jehu sent letters to Samaria, to the rulers of the town, and to the responsible men, and to those who had the care of the sons of Ahab, saying,

Then he sent them a second letter, saying, If you are on my side, and if you will do my orders, come to me at Jezreel by this time tomorrow, with the heads of your master's sons. Now the king's seventy sons were with the great men of the town, who had the care of them.

And when the letter came to them, they took the king's sons and put them to death, all the seventy, and put their heads in baskets and sent them to him at Jezreel.