The Gelfond-Schneider constant is the number 
(OEIS A007507)
that is known to be transcendental by Gelfond's theorem. Both the Gelfond-Schneider constant
and Gelfond's constant 
were singled out in the 7th of Hilbert's
problems as examples of numbers whose transcendence was an open problem (Hilbert
1902, p. 456).
Gelfond-Schneider Constant
See also
Gelfond's Constant, Gelfond's Theorem, Pythagoras's ConstantExplore with Wolfram|Alpha
References
Courant, R. and Robbins, H. What Is Mathematics?: An Elementary Approach to Ideas and Methods, 2nd ed. Oxford, England: Oxford University Press, p. 107, 1996.Hilbert, D. "Mathematical Problems." Bull. Amer. Math. Soc. 8, 437-479, 1902. https://doi.org/10.1090/S0002-9904-1902-00923-3.Sloane, N. J. A. Sequence A007507/M1560 in "The On-Line Encyclopedia of Integer Sequences."Wells, D. The Penguin Dictionary of Curious and Interesting Numbers. Middlesex, England: Penguin Books, p. 45, 1986.Referenced on Wolfram|Alpha
Gelfond-Schneider ConstantCite this as:
Weisstein, Eric W. "Gelfond-Schneider Constant." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Gelfond-SchneiderConstant.html