This person's paper "On the Number of Primes Less Than a
Soon after Lobachevsky [loe-bah-CHEV-skee] developed hyperbolic geometry, this person developed elliptic geometry. This person's namesake geometry is differential, allowing for the use of his namesake metric and manifolds. This person's paper "On the Number of Primes Less Than a Given Magnitude" introduced a function named his zeta function. Name this German mathematician whose name is used for the integral approximation method that uses rectangles.
Soon after Lobachevsky [loe-bah-CHEV-skee] developed hyperbolic geometry, this person developed elliptic geometry.
Bernhard Riemann