A member of the smallest algebraically closed subfield 
of 
which is closed under the exponentiation
and logarithm operations.
Liouvillian Number
See also
Elementary NumberExplore with Wolfram|Alpha
References
Chow, T. Y. "What is a Closed-Form Number." Amer. Math. Monthly 106, 440-448, 1999.Richardson, D. "The Elementary Constant Problem." In Proc. Internat. Symp. on Symbolic and Algebraic Computation, Berkeley, July 27-29, 1992 (Ed. P. S. Wang). ACM Press, 1992.Ritt, J. Integration in Finite Terms: Liouville's Theory of Elementary Models. New York: Columbia University Press, 1948.Referenced on Wolfram|Alpha
Liouvillian NumberCite this as:
Weisstein, Eric W. "Liouvillian Number." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/LiouvillianNumber.html