Gelfond's constant

2009, Samuel W. Gilbert, The Riemann Hypothesis and the Roots of the Riemann Zeta Function, BookSurge Publishing, page 93, Gelfond's constant satisfies the identity e^π=(-1)⁻ⁱ Therefore, the roots of the Riemann zeta function are defined by geometrical constraints of the discrete partial sums of the Dirichlet series terms by continuous and geometrically equivalent envelopes defined by powers of Gelfond's constant.

and we have the promised appearance of Gelfond's constant.

2016, Ravi P. Agarwal, Hans Agarwal, Syamal K. Sen, Birth, growth and computation of pi to ten trillion digits, David H. Bailey, Jonathan M. Borwein (editors, Pi: The Next Generation, Springer, page 403, Alexander Osipovich Gelfond (1906-1968) was a Soviet mathematician. He proved that e^π (Gelfond's constant) is transcendental, but nothing yet is known about the nature of the numbers π + e, πe, or πᵉ.