The Friday File: In 1951, the longest known prime number was 79 digits. It passed 10,000 digits in 1980, 100,000 digits in the early 1990s, 1,000,000 digits in the late 1990s, and is now over 23 million digits. There is a prize of $150,000 for the person who finds the first prime with 100 million digits; $250,000 for the first prime with 1 billion digits. What are you waiting for?