For almost twenty years, Hardy later told Erdos, their theorem seemed dead in the water, no progress being made in improving it. Then, in 1934, the problem was resurrected, and in 1939 Erdos and Mark Kac were led to a theorem that took it much further. It was only then that mathematicians could look back and pronounce the Hardy-Ramanujan paper of 1917 the founding document of the field that became known as probabilistic number theory.
