Weisstein, Eric W. (编). Transcendental Number. at MathWorld--A Wolfram Web Resource. Wolfram Research, Inc.(英语). gives , based on
Nesterenko, Yu. V. "On Algebraic Independence of the Components of Solutions of a System of Linear Differential Equations." Izv. Akad. Nauk SSSR, Ser. Mat. 38, 495–512, 1974. English translation in Math. USSR 8, 501–518, 1974.