'Seventy' in the Bible

Now Ahab had seventy sons in Samaria. Jehu wrote letters, and sent to Samaria, to the rulers of Jezreel, even the elders, and to those who brought up [the sons of] Ahab, saying,

Then he wrote a letter the second time to them, saying, "If you are on my side, and if you will listen to my voice, take the heads of the men your master's sons, and come to me to Jezreel by tomorrow this time." Now the king's sons, being seventy persons, were with the great men of the city, who brought them up.

It happened, when the letter came to them, that they took the king's sons, and killed them, even seventy persons, and put their heads in baskets, and sent them to him to Jezreel.