In Cogitata Physica-Mathematica the French monk Marin Mersenne makes a conjecture (Mersenne conjecture): the numbers 2^n – 1 are prime for n=2, 3, 5, 7, 13, 17, 19, 31, 67, 127, 257; it took more than 3 centuries to prove that these numbers were really prime; by the end of the 20th century the list of Mersenne primes had already expanded to the number 2^6972593-1 (2098960 digits).
