OFFSET
0,1
COMMENTS
Tetration x^^n is defined recursively: x^^0 = 1, x^^n = x^(x^^(n-1)). Note that sqrt(2)^^inf = lim_{n->inf} sqrt(2)^^n = 2. Asymptotically, sqrt(2)^^n = 2 - O(log(2)^n). This constant is the coefficient in the O(log(2)^n) term. Furthermore, sqrt(2)^^n = 2 - a*log(2)^n + (a^2/(4*(1 - 1/log(2))))*log(2)^(2*n) + O(log(2)^(3*n)).
LINKS
Eric Weisstein's World of Mathematics, Power Tower
Wikipedia, Tetration
FORMULA
a = 2*sqrt(2)*A260691/(1-log(2)).
EXAMPLE
0.63209866105082925035545064599078...
MATHEMATICA
RealDigits[SequenceLimit[1`200 Table[(2 - Power @@ Table[Sqrt[2], {n}])/Log[2]^n, {n, 1, 200}]], 10, 100][[1]]
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Vladimir Reshetnikov, Oct 14 2016
STATUS
approved