For ten points, identify this Swiss mathematician, a formula named for whom is used to de ne complex exponentiation.
With Tricomi, this mathematician names the partial di erential equation uxx + xuyy = 0. In music theory, this man and Fokker name any musical scale whose pitches are generated from products of a set of prime numbers. There are either 65 or 66 of this man's idoneal numbers, depending on the truth of the Riemann Hypothesis. An identity named for this man states that the productof two sums of four   squares is itself a sum of four squares, and this man names, with Mascheroni, a constant equal to the limit of the di erence between the harmonic series and the natural logarithm. For ten points, identify this Swiss mathematician, a formula named for whom is used to de ne complex exponentiation.
With Tricomi, this mathematician names the partial di erential equation uxx + xuyy = 0.
Leonard Euler