The first letter, dated 21 November 1804, discussed Gauss' and presented some of Germain's work on Fermat's Last Theorem. In the letter, Germain claimed to have proved the theorem for "n" = "p" − 1, where "p" is a prime number of the form "p" = 8"k" + 7. However, her proof contained a weak assumption, and Gauss' reply did not comment on Germain's proof. Around 1807 (sources differ), during the Napoleonic wars, the French were occupying the German town of Braunschweig, where Gauss lived. Germain, concerned that he might suffer the fate of Archimedes, wrote to General Pernety, a family friend, requesting that he ensure Gauss' safety. General Pernety sent a chief of a battalion to meet with Gauss personally to see that he was safe. As it turned out, Gauss was fine, but he was confused by the mention of Sophie's name. Three months after the incident, Germain disclosed her true identity to Gauss. He replied:  How can I describe my astonishment and admiration on seeing my esteemed correspondent M. Le Blanc metamorphosed into this celebrated person ... when a woman, because of her sex, our customs and prejudices, encounters infinitely more obstacles than men in familiarising herself with [number theory's] knotty problems, yet overcomes these fetters and penetrates that which is most hidden, she doubtless has the most noble courage, extraordinary talent, and superior genius. Gauss' letters to Olbers show that his praise for Germain was sincere. In the same 1807 letter, Germain claimed that if formula_1 is of the form formula_2, then formula_3 is also of that form. Gauss replied with a counterexample: formula_4 can be written as formula_5, but formula_6 cannot. Although Gauss thought well of Germain, his replies to her letters were often delayed, and he generally did not review her work. Eventually his interests turned away from number theory, and in 1809 the letters ceased. Despite the friendship of Germain and Gauss, they never met. When Germain's correspondence with Gauss ceased, she took interest in a contest sponsored by the Paris Academy of Sciences concerning Ernst Chladni's experiments with vibrating metal plates. The object of the competition, as stated by the Academy, was "to give the mathematical theory of the vibration of an elastic surface and to compare the theory to experimental evidence".