15. Last January 7, 2016, a team from the University of Central Missouri headed by Curtis Cooper discovered the largest prime number known so far:
$$
2^{74,207,281}-1
$$
which contains over 22.3 million digits. Curtis Cooper is part of a large collaborative project called GIMPS, where mathematicians use their computers to look for prime numbers of the form 1 less than a power of 2 . What is the meaning of GIMPS?
Answer: Great Internet Mersenne Prime Search