Riemann and the Cauchy-Hadamard formula for the convergence of power series (Q1323509)

The well known formula for the radius of convergence of a power series is stated and proved 1821 in Cauchy's book `Cours d'analyse'. It was rediscovered by Hadamard and published in a Comptes Rendus note of 1888. Therefore it is customarily called the Cauchy-Hadamard-formula. The authors of the paper under review have discovered the surprising fact that Riemann in his notes of 1855 and in his lecture of November 1856 had stated and proved the Cauchy-Hadamard-formula. They produce the relevant parts of his Nachlaß and some manuscripts of his students E. Schering and R. Dedekind. At the end of the paper the authors discuss the question of ``Why did Cauchy's formula fall into oblivion''?