'Seventy' in the Bible

Ahab had seventy sons in Samaria, and Jehu wrote letters, and he sent them to Samaria to the officials of Jezreel, to the elders and to the guardians of Ahab, saying,

Then he wrote to them a second letter, saying, "If you [are] for me, and you [are] listening to my voice, take the heads of the men of the sons of your master and come to me at [this] time tomorrow at Jezreel." Now the sons of the king, seventy men, [were] with the leaders of the city who were raising them.

When the letter came to them, they took the sons of the king, and they killed seventy men. Then they put their heads in baskets and sent them to him at Jezreel.