%I #10 Mar 30 2012 19:00:09
%S 1,7,8,3,8,1,4,2,5,1,7,7,0,4,6,1,9,2,1,9,0,1,2,7,6,7,1,1,3,1,3,2,8,3,
%T 7,9,1,7,0,7,3,6,5,8,3,4,6,7,9,5,1,1,8,2,0,8,7,8,2,4,7,7,6,8,7,5,6,4,
%U 2,8,5,4,6,2,2,2,4,3,7,1,0,2,8,6,1,2,6,6,2,2,2,7,8,2,3,2,3,7,2,7
%N Decimal expansion of x with 0 < x < y and x^y = y^x = 17.
%C Given z > 0, there exist positive real numbers x < y with x^y = y^x = z, if and only if z > e^e. In that case, (x,y) = ((1 + 1/t)^t,(1 + 1/t)^(t+1)) for some t > 0. For example, t = 1 gives 2^4 = 4^2 = 16 > e^e. When x^y = y^x = 17, at least one of x and y is transcendental. See Sondow and Marques 2010, pp. 155-157.
%H J. Sondow and D. Marques, <a href="http://ami.ektf.hu/uploads/papers/finalpdf/AMI_37_from151to164.pdf">Algebraic and transcendental solutions of some exponential equations</a>, Annales Mathematicae et Informaticae, 37 (2010), 151-164.
%e x=1.7838142517704619219012767113132837917073658346795118208782477687564285462224371...
%t x[t_] := (1 + 1/t)^t; y[t_] := (1 + 1/t)^(t + 1); t = t/. FindRoot[ x[t]^y[t] == 17, {t, 1}, WorkingPrecision -> 120]; RealDigits[ x[t], 10, 100] // First
%Y Cf. A073226 (e^e), A194556 ((9/4)^(27/8) = (27/8)^(9/4)), A194557 (sqrt(3)^sqrt(27) = sqrt(27)^sqrt(3)), A194623 (y with 0 < x < y and x^y = y^x = 17).
%K nonn,cons
%O 1,2
%A _Jonathan Sondow_, Aug 30 2011